Solar cell and solar cell panel including the same

ABSTRACT

A solar cell is disclosed. The disclosed solar cell includes a semiconductor substrate, a conductive region disposed in or on the semiconductor substrate, and an electrode including a plurality of finger lines connected to the conductive region, and formed to extend in a first direction while being parallel, and 6 or more bus bar lines formed to extend in a second direction crossing the first direction. Each bus bar line has a width of 35 to 350 μm at at least a portion thereof. Each bus bar line has a distance between opposite ends thereof in the second direction smaller than a distance between outermost ones of the finger lines respectively disposed at opposite sides in the second direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Korean PatentApplication No. 10-2014-0131958, filed on Sep. 30, 2014, Korean PatentApplication No. 10-2015-0061334, filed on Apr. 30, 2015 and KoreanPatent Application No. 10-2015-0105965, filed on Jul. 27, 2015, in theKorean Intellectual Property Office. All these applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate to a solar cell and a solarcell panel including the same, and more particularly to solar cellsconnected by leads and a solar cell panel including the same.

2. Description of the Related Art

Recently, as existing energy resources such as petroleum and coal aredepleted, interest in alternative energy sources is increasing. Inparticular, a solar cell is highlighted as a next-generation cellcapable of converting solar energy into electric energy.

A plurality of solar cells as mentioned above is connected in series orin parallel by a plurality of ribbons, and is then packaged through apackaging process, for protection thereof, thereby forming a solar cellpanel. Since such a solar cell panel must perform generation for a longperiod of time in various environments, the solar cell panel shouldsecure long-term reliability. In conventional instances, a plurality ofsolar cells is connected by ribbons, as mentioned above.

However, when solar cells are connected using ribbons having a greatwidth of about 1.5 mm, shading loss may be generated due to such a greatwidth of the ribbons. For this reason, the number of ribbons used forthe solar cells should be reduced. Furthermore, the ribbons exhibitinferior attachment strength, or the solar cells may exhibit anincreased degree of bending due to the ribbons. In such an instance,there is a limitation in enhancing the output power of the solar cellpanel. In addition, the ribbons may be detached from the solar cells, orthe solar cells may be damaged. As a result, the solar cell panel mayexhibit decreased reliability.

SUMMARY OF THE INVENTION

Therefore, the embodiments of the present invention have been made inview of the above problems, and it is an object of the embodiments ofthe present invention to provide a solar cell capable of enhancing theoutput power and reliability of a solar cell panel, and a solar cellpanel including the same.

In accordance with an aspect of the present invention, the above andother objects can be accomplished by the provision of a solar cellincluding a semiconductor substrate, a conductive region disposed in oron the semiconductor substrate, and an electrode including a pluralityof finger lines connected to the conductive region, and formed to extendin a first direction while being parallel, and 6 or more bus bar linesformed to extend in a second direction crossing the first direction,each of the bus bar lines having a width of 35 to 350 μm at at least aportion thereof, wherein the each of the bus bar lines has a distancebetween opposite ends thereof in the second direction smaller than adistance between outermost ones of the finger lines respectivelydisposed at opposite sides of the semiconductor substrate in the seconddirection.

In accordance with another aspect of the present invention, there isprovided a solar cell panel including a plurality of solar cells eachincluding a photoelectric converter, and a first electrode and a secondelectrode connected to the photoelectric converter, and a plurality ofleads for connecting neighboring ones of the plurality of solar cellssuch that the first electrode in one of the neighboring solar cells isconnected to the second electrode in the other of the neighboring solarcells, wherein each of the first electrode and the second electrodeincludes a plurality of finger lines formed to extend in a firstdirection while being parallel, and 6 or more bus bar lines formed toextend in a second direction crossing the first direction, the pluralityof leads have a diameter or width of 250 to 500 μm, and includes 6 ormore leads arranged at one surface side of the solar cell while beingconnected to the bus bar lines, respectively, each of the bus bar lineshas a distance between opposite ends thereof in the second directionsmaller than a distance between outermost ones of the plurality offinger lines respectively disposed at opposite sides of thephotoelectric converter in the second direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of theembodiments of the present invention will be more clearly understoodfrom the following detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a perspective view illustrating a solar cell panel accordingto an embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1;

FIG. 3 is a sectional view illustrating an example of the solar cellincluded in the solar cell panel of FIG. 1;

FIG. 4 is a sectional view illustrating another example of the solarcell included in the solar cell panel of FIG. 1;

FIG. 5 is a perspective view briefly illustrating a first solar cell anda second solar cell, which are connected by leads, in the solar cellpanel of FIG. 1;

FIG. 6 illustrates one lead before attachment thereof to electrodes ofone solar cell illustrated in FIG. 1, through a perspective view and asectional view;

FIG. 7 is a sectional view illustrating the lead attached to padsections of the electrode in the solar cell illustrated in FIG. 1;

FIG. 8 is a cross-sectional view taken along line VIII-VIII in FIG. 5;

FIG. 9 is a plan view illustrating one solar cell included in the solarcell panel of FIG. 1 and leads connected thereto;

FIG. 10 is a plan view illustrating the solar cell included in the solarcell panel of FIG. 1;

FIG. 11 is a photograph of cross-sections of solar cells, to which leadshaving different widths are attached, respectively;

FIG. 12 is a graph depicting measured results of attachment force of thelead to an end of the electrode while varying the width of the lead andan edge distance;

FIG. 13 is a diagram depicting outputs of the solar cell panel measuredwhile varying the width of each lead and the number of leads;

FIG. 14 is a plan view illustrating a portion of the front surface of asolar cell according to another embodiment of the present invention;

FIG. 15 is a plan view illustrating a portion of the front surface of asolar cell according to another embodiment of the present invention; and

FIG. 16 is a graph depicting measured results of attachment forcemeasured while pulling a lead attached to a solar cell using anexperimental device.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the example embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The present invention may, however, be embodied in manyalternate forms and should not be construed as limited to theembodiments set forth herein.

In the drawings, illustration of parts having no concern with theembodiments of the present invention is omitted for clarity andsimplicity of description. The same reference numerals designate thesame or very similar elements throughout the specification. In thedrawings, the thicknesses, widths or the like of elements areexaggerated or reduced for clarity of description, and should not beconstrued as limited to those illustrated in the drawings.

It will be understood that the terms “comprises” and/or “comprising,” or“includes” and/or “including” when used in the specification, specifythe presence of stated elements, but do not preclude the presence oraddition of one or more other elements. In addition, it will beunderstood that, when an element such as a layer, film, region, or plateis referred to as being “on” another element, it can be directlydisposed on another element or can be disposed such that an interveningelement is also present therebetween. Accordingly, when an element suchas a layer, film, region, or plate is disposed “directly on” anotherelement, this means that there is no intervening element between the twoelements.

Hereinafter, solar cells and solar cell panels including the sameaccording to embodiments of the present invention will be described indetail with reference to the accompanying drawings.

FIG. 1 is a perspective view illustrating a solar cell panel accordingto an embodiment of the present invention. FIG. 2 is a cross-sectionalview taken along line II-II in FIG. 1.

Referring to FIGS. 1 and 2, the solar cell panel according to theillustrated embodiment, which is designated by reference numeral “100”,includes a plurality of solar cells 150, and leads 142 for electricallyconnecting the solar cells 150. The solar cell panel 100 also includes asealant 130 for enclosing and sealing the solar cells 150 and leads 142,a front substrate 110 disposed at a front side of the solar cells 150,and a back substrate 200 disposed at a backside of the solar cells 150over the sealant 130. This will be described in more detail.

First, each solar cell 150 may include a photoelectric converter forconverting solar energy into electric energy, and an electrodeelectrically connected to the photoelectric converter, to collectcurrent, for transfer of the collected current. The solar cells 150 maybe electrically connected in series, in parallel, or in series-parallelby the leads 142. In detail, longitudinally neighboring ones of thesolar cells 150 are electrically connected by corresponding ones of theleads 142 and, as such, the solar cells 150 form strings extending inthe longitudinal direction.

The bus ribbons 145 connect opposite ends of the solar cell strings, indetail, ends of the leads 142 thereof, in an alternating manner. The busribbons 145 may be arranged at opposite ends of the solar cell strings,to extend in a direction crossing the solar cell strings. The busribbons 145 may connect adjacent ones of the solar cell strings, orconnect the solar cell strings to a junction box for preventing backwardflow of current. The material, shape, and connecting structure of thebus ribbons 145 may be diverse and, as such, the embodiments of thepresent invention are not limited thereto.

The sealant 130 may include a first sealant 131 disposed at the frontside of the solar cells 150, and a second sealant 132 disposed at thebackside of the solar cells 150. The first sealant 131 and secondsealant 132 block permeation of moisture, oxygen or both, which mayadversely affect the solar cells 150, and enable chemical coupling ofcomponents of the solar cell panel 100. The solar cell panel 100 mayhave an integrated structure. This may be achieved by arranging the backsubstrate 200, second sealant 132, solar cells 150, first sealant 131and front substrate 110 in this order, and then applying heat and/orpressure or the like to the resultant structure through a laminationprocess.

As the first sealant 131 and second sealant 132, ethylene vinyl acetate(EVA) copolymer resin, polyvinyl butyral, silicon resin, ester-basedresin, olefin-based resin, or the like may be used. Of course, theembodiments of the present invention are not limited to such materials.Accordingly, the first and second sealants 131 and 132 may be formed,using various other materials, in accordance with a method other thanlamination. In this instance, the first and second sealants 131 and 132have optical transparency, to allow light incident through the backsubstrate 200 or light reflected from the back substrate 200 to reachthe solar cells 150.

The front substrate 110 is disposed on the first sealant 131 and, assuch, constitutes a front surface of the solar cell panel 100. The frontsubstrate 110 may be made of a material having a strength capable ofprotecting the solar cells 150 from external impact or the like andoptical transparency capable of allowing transmission of light such assunlight. For example, the front substrate 110 may be constituted by aglass substrate or the like. In this instance, the front substrate 110may be constituted by a reinforced glass substrate, for strengthenhancement. In addition, various variations may be applied to the frontsubstrate 110. For example, the front substrate 110 may additionallycontain various materials capable of improving various characteristics.Alternatively, the front substrate 110 may be a sheet or film made ofresin or the like. That is, the embodiments of the present invention arenot limited as to the material of the front substrate 110, and the frontsubstrate 110 may be made of various materials.

The back substrate 200 is a layer disposed on the second sealant 132, toprotect the solar cells 150 at the backside thereof. The back substrate200 may have waterproof, insulation, and ultraviolet blocking functions.

The back substrate 200 may have a strength capable of protecting thesolar cells 150 from external impact or the like. The back substrate 200may also have characteristics allowing transmission of light orreflection of light in accordance with a desired structure of the solarcell panel 150. For example, in a structure of the solar cell panel 150,in which light is incident through the back substrate 200, the backsubstrate 200 may be made of a transparent material. On the other hand,in a structure of the solar cell panel 150, in which light is reflectedby the back substrate 200, the back substrate 200 may be made of anopaque material, a reflective material, or the like. For example, theback substrate 200 may have a substrate structure made of glass.Alternatively, the back substrate 200 may have a film or sheet structureor the like. For example, the back substrate 200 may be ofTedlar/PET/Tedlar (TPT) type or may have a structure in whichpolyvinylidene fluoride (PVDF) resin or the like is formed over at leastone surface of polyethylene terephthalate (PET). PVDF, which is apolymer having a structure of (CH₂CF₂)_(n), has a double fluorinemolecular structure and, as such, has excellent mechanical properties,weather resistance and ultraviolet resistance. However, the embodimentsof the present invention are not limited as to the material of the backsubstrate 200.

Hereinafter, an example of one solar cell included in the solar cellpanel according to the illustrated embodiment of the present inventionwill be described in more detail with reference to FIG. 3.

Referring to FIG. 3, the solar cell 150 according to the illustratedembodiment includes a semiconductor substrate 160 including a baseregion 10, conductive regions 20 and 30 formed in the semiconductorsubstrate 160 or on the semiconductor substrate 160, and electrodes 42and 44 respectively connected to the conductive regions 20 and 30. Inthis instance, the conductive regions 20 and 30 may include afirst-conduction-type conductive region 20 having a first conductivityand a second-conduction-type conductive region 30 having a secondconductivity. The electrodes 42 and 44 may include a first electrode 42connected to the first-conduction-type conductive region 20 and a secondelectrode 44 connected to the second-conduction-type conductive region30. The solar cell 150 may further include a first passivation film 22,an anti-reflective film 24, a second passivation film 32, etc.

The semiconductor substrate 160 may be made of crystallinesemiconductor. For example, the semiconductor substrate 160 may be madeof a single-crystalline or polycrystalline semiconductor (for example, asingle-crystalline or polycrystalline silicon). In particular, thesemiconductor substrate 160 may be made of a single-crystallinesemiconductor (for example, a single-crystalline semiconductor wafer, inmore detail, a single-crystalline silicon wafer). When the semiconductorsubstrate 160 is made of a single-crystalline semiconductor (forexample, a single-crystalline silicon), the solar cell 150 exhibitsreduced defects because the solar cell 150 is based on the semiconductorsubstrate 160, which has high crystallinity. Thus, the solar cell 150may have excellent electrical characteristics.

The front and/or back surface of the semiconductor substrate 160 mayhave an uneven surface structure having protrusions and grooves throughtexturing. For example, the protrusions and grooves have a pyramid shapehaving an outer surface constituted by a (111)-oriented surface of thesemiconductor substrate 160 while having an irregular size. For example,when the front surface of the semiconductor substrate 160 has increasedsurface roughness in accordance with formation of protrusions andgrooves through texturing, it may be possible to reduce reflectance oflight incident through the front surface of the semiconductor substrate160. Accordingly, an amount of light reaching a pn junction formed bythe base region 10 and first-conduction-type conductive region 20 may beincreased and, as such, shading loss may be minimized. However, theembodiments of the present invention are not limited to theabove-described structure. The semiconductor substrate 160 may not have,at the front and back surfaces thereof, protrusions and grooves formedthrough texturing.

The base region 10 of the semiconductor substrate 160 may be doped witha second-conduction-type dopant at a relatively low doping concentrationand, as such, has the second conductivity. For example, the base region10 may be arranged farther from the front surface of the semiconductorsubstrate 160 or closer to the back surface of the semiconductorsubstrate 160 than the first-conduction-type conductive region 20. Inaddition, the base region 10 may be arranged closer to the front surfaceof the semiconductor substrate 160 or farther from the back surface ofthe semiconductor substrate 160 than the second-conduction-typeconductive region 30. Of course, the embodiments of the presentinvention are not limited to such arrangement, and the location of thebase region 10 may be varied.

In this instance, the base region 10 may be made of a crystallinesemiconductor containing a second-conduction-type dopant, for example, asingle-crystalline or polycrystalline semiconductor (for example, asingle-crystalline or polycrystalline silicon) containing asecond-conduction-type dopant. In particular, the base region 10 may bemade of a single-crystalline semiconductor (for example, asingle-crystalline semiconductor wafer, in more detail, asingle-crystalline silicon wafer) containing a second-conduction-typedopant.

The second conduction type may be n-type or p-type. When the base region10 has n-type conductivity, the base region 10 may be made of asingle-crystalline or polycrystalline semiconductor doped with a Group-Velement such as phosphorous (P), arsenic (As), bismuth (Bi) or antimony(Sb). On the other hand, when the base region 10 has p-typeconductivity, the base region 10 may be made of a single-crystalline orpolycrystalline semiconductor doped with a Group-III element such asboron (B), aluminum (Al), gallium (Ga), or indium (In).

Of course, the embodiments of the present invention are not limited tothe above-described materials, and the base region 10 and thesecond-conduction-type dopant may be constituted by various materials.

For example, the base region 10 may have n-type conductivity. Then, thefirst-conduction-type conductive region 20, which forms a pn junctiontogether with the base region 10, has p-type conductivity. When light isirradiated to such a pn junction, electrons produced in accordance witha photoelectric effect migrate toward the back surface of thesemiconductor substrate 160 and, as such, are collected by the secondelectrode 44. Meanwhile, holes migrate toward the front surface of thesemiconductor substrate 160 and, as such, are collected by the firstelectrode 42. As a result, electric energy is generated. Then, holeshaving a lower movement rate than electrons migrate toward the backsurface of the semiconductor substrate 160, rather than the frontsurface of the semiconductor substrate 160 and, as such, photoelectricconversion efficiency may be enhanced. Of course, the embodiments of thepresent invention are not limited to the above-described conditions, andthe base region 10 and the second-conduction-type conductive region 30may have p-type conductivity, and the first-conduction-type conductiveregion 20 may have n-type conductivity.

The first-conduction-type conductive region 20, which has the firstconductivity opposite that of the base region 10, may be formed at thefront surface side of the semiconductor substrate 160. Thefirst-conduction-type conductive region 20 forms a pn junction togetherwith the base region 10 and, as such, constitutes an emitter region toproduce carriers in accordance with a photoelectric effect.

In the illustrated embodiment, the first-conduction-type conductiveregion 20 may be constituted by a doped region constituting a portion ofthe semiconductor substrate 160. In this instance, thefirst-conduction-type conductive region 20 may be made of a crystallinesemiconductor containing a first-conduction-type dopant. For example,the first-conduction-type conductive region 20 may be made of asingle-crystalline or polycrystalline semiconductor (for example, asingle-crystalline or polycrystalline silicon) containing afirst-conduction-type dopant. In particular, the first-conduction-typeconductive region 20 may be made of single-crystalline semiconductor(for example, a single-crystalline semiconductor wafer, in more detail,a single-crystalline silicon wafer) containing a first-conduction-typedopant. When the first-conduction-type conductive region 20 constitutesa portion of the semiconductor substrate 160, as described above,junction characteristics of the base region 10 and first-conduction-typeconductive region 20 may be enhanced.

Of course, the embodiments of the present invention are not limited tothe above-described conditions and, the first-conduction-type conductiveregion 20 may be formed on the semiconductor substrate 160, separatelyfrom the semiconductor substrate 160. In this instance, thefirst-conduction-type conductive region 20 may be constituted by asemiconductor layer having a crystalline structure different from thatof the semiconductor substrate 160, for easy formation thereof on thesemiconductor substrate 160. For example, the first-conduction-typeconductive region 20 may be formed by doping an amorphous semiconductor,microcrystalline semiconductor, or polycrystalline semiconductor (forexample, an amorphous silicon, microcrystalline silicon, orpolycrystalline silicon), which may be easily manufactured throughvarious methods such as deposition, with a first-conduction-type dopant.Of course, other variations are possible.

The first-conduction-type may be p-type or n-type. When thefirst-conduction-type conductive region 20 has p-type conductivity, thefirst-conduction-type conductive region 20 may be made of asingle-crystalline or polycrystalline semiconductor doped with aGroup-III element such as boron (B), aluminum (Al), gallium (Ga), orindium (In). On the other hand, when the first conduction type hasn-type conductivity, the first-conduction-type conductive region 20 maybe made of a single-crystalline or polycrystalline semiconductor dopedwith a Group-V element such as phosphorous (P), arsenic (As), bismuth(Bi) or antimony (Sb). For example, the first-conduction-type conductiveregion 20 may be a single-crystalline or polycrystalline semiconductordoped with boron. Of course, the embodiments of the present inventionare not limited to the above-described materials, and various materialsmay be used as the first-conduction-type dopant.

In the drawings, the first-conduction-type conductive region 20 isillustrated as having a homogeneous structure having a uniform dopingconcentration throughout the first-conduction-type conductive region 20.Of course, the embodiments of the present invention are not limited tothe above-described structure. In another embodiment, thefirst-conduction-type conductive region 20 may have a selectivestructure, as illustrated in FIG. 4.

Referring to FIG. 4, the first-conduction-type conductive region 20,which has a selective structure, may include a first portion 20 a formedadjacent to the first electrode 42, to contact the first electrode 42,and a second portion 20 b formed at the remaining portion of thefirst-conduction-type conductive region 20, namely, a portion of thefirst-conduction-type conductive region 20, except for the first portion20 a.

The first portion 20 a may have a high doping concentration and, assuch, may have relatively low resistance. The second portion 20 b mayhave a lower doping concentration that the first portion 20 a and, assuch, may have relatively high resistance. The first portion 20 a mayhave a greater thickness than the second portion 20 b. That is, thejunction depth of the first portion 20 a may be greater than that of thesecond portion 20 b.

Thus, in the illustrated embodiment, a shallow emitter is realized byforming the second portion 20 b having relatively high resistance at aportion of the first-conduction-type conductive region 20, except forthe first portion 20 a. Accordingly, the current density of the solarcell 150 may be enhanced. In addition, it may be possible to reducecontact resistance of the first-conduction-type conductive region 20 tothe first electrode 42 by forming the first portion 20 a havingrelatively low resistance at a portion of the first-conduction-typeconductive region 20 adjacent to the first electrode 42. Accordingly,maximal efficiency of the solar cell 150 may be achieved.

The first-conduction-type conductive region 20 may have variousstructures and various shapes other than the above-described structuresand shapes.

Again referring to FIG. 3, the second-conduction-type conductive region30, which has the second conductivity identical to that of the baseregion 10 while having a higher doping concentration than the baseregion 10, may be formed at the back surface side of the semiconductorsubstrate 160. The second-conduction-type conductive region 30 forms aback surface field region, which generates a back surface field, toprevent loss of carriers caused by re-coupling (or recombination)thereof at a surface of the semiconductor substrate 160 (in more detail,the back surface of the semiconductor substrate 160).

In the illustrated embodiment, the second-conduction-type conductiveregion 30 may be constituted by a doped region constituting a portion ofthe semiconductor substrate 160. In this instance, thesecond-conduction-type conductive region 30 may be made of a crystallinesemiconductor containing a second-conduction-type dopant. For example,the second-conduction-type conductive region 30 may be made of asingle-crystalline or polycrystalline semiconductor (for example, asingle-crystalline or polycrystalline silicon) containing asecond-conduction-type dopant. In particular, the second-conduction-typeconductive region 30 may be made of single-crystalline semiconductor(for example, a single-crystalline semiconductor wafer, in more detail,a single-crystalline silicon wafer) containing a second-conduction-typedopant. When the second-conduction-type conductive region 30 constitutesa portion of the semiconductor substrate 160, as described above,junction characteristics of the base region 10 and thesecond-conduction-type conductive region 30 may be enhanced.

Of course, the embodiments of the present invention are not limited tothe above-described conditions and, the second-conduction-typeconductive region 30 may be formed on the semiconductor substrate 160,separately from the semiconductor substrate 160. In this instance, thesecond-conduction-type conductive region 30 may be constituted by asemiconductor layer having a crystalline structure different from thatof the semiconductor substrate 160, for easy formation thereof on thesemiconductor substrate 160. For example, the second-conduction-typeconductive region 30 may be formed by doping an amorphous semiconductor,microcrystalline semiconductor, or polycrystalline semiconductor (forexample, an amorphous silicon, microcrystalline silicon, orpolycrystalline silicon), which may be easily manufactured throughvarious methods such as deposition, with a second-conduction-typedopant. Of course, other variations are possible.

The second-conduction-type may be n-type or p-type. When thesecond-conduction-type conductive region 30 has n-type conductivity, thesecond-conduction-type conductive region 30 may be made of asingle-crystalline or polycrystalline semiconductor doped with a Group-Velement such as phosphorous (P), arsenic (As), bismuth (Bi) or antimony(Sb). On the other hand, the second conduction type has p-typeconductivity, the second-conduction-type conductive region 30 may bemade of a single-crystalline or polycrystalline semiconductor doped witha Group-III element such as boron (B), aluminum (Al), gallium (Ga), orindium (In). For example, the second-conduction-type conductive region30 may be a single-crystalline or polycrystalline semiconductor dopedwith phosphorous. Of course, the embodiments of the present inventionare not limited to the above-described materials, and various materialsmay be used as the second-conduction-type dopant. In addition, thesecond-conduction-type dopant of the second-conduction-type conductiveregion 30 may be identical to the second-conduction-type dopant of thebase region 10 or may differ from the second-conduction-type dopant ofthe base region 10.

In this embodiment, the second-conduction-type conductive region 30 isillustrated as having a homogeneous structure having a uniform dopingconcentration throughout the second-conduction-type conductive region30. Of course, the embodiments of the present invention are not limitedto the above-described structure. In another embodiment, thesecond-conduction-type conductive region 30 may have a selectivestructure. In the selective structure, the second-conduction-typeconductive region 30 may have a high doping concentration, a greatjunction depth, and low resistance at a portion thereof adjacent to thesecond electrode 44 while having a low doping concentration, a smalljunction depth, and high resistance at the remaining portion of thesecond-conduction-type conductive region 30. The selective structure ofthe second-conduction-type conductive region 30 is identical or similarto that of the first-conduction-type conductive region 20 illustrated inFIG. 4 and, as such, the description given of the first-conduction-typeconductive region 20 with reference to FIG. 4 in association with theselective structure may be applied to the second-conduction-typeconductive region 30. In another embodiment, the second-conduction-typeconductive region 30 may have a local structure, as illustrated in FIG.4.

Referring to FIG. 4, the second-conduction-type conductive region 30,which has a local structure, may include a first portion 30 a locallyformed at a portion of the second-conduction-type conductive region 30connected to the second electrode 44. Accordingly, thesecond-conduction-type conductive region 30 exhibits reduced contactresistance to the second electrode 44 at the portion thereof connectedto the second electrode 44 and, as such, may have excellent fill factor(FF) characteristics. On the other hand, no second-conduction-typeconductive region 30 constituted by a doped region is formed at a regionnot connected to the second electrode 44 and, as such, re-couplingpossibly occurring at the doped region may be reduced. Accordingly,short-circuit current density Jsc and open-circuit voltage may beenhanced. In addition, excellent internal quantum efficiency (IQE) maybe exhibited at the region where no second-conduction-type conductiveregion is formed and, as such, characteristics associated withlong-wavelength light may be excellent. Accordingly, it may be possibleto greatly enhance characteristics associated with long-wavelengthlight, as compared to the homogenous structure and selective structurehaving a doped region throughout the structure. Thus, thesecond-conduction-type conductive region 30, which has the localstructure as described above, may be excellent in terms of fill factor,short-circuit current density, and open-circuit voltage and, as such,may achieve an enhancement in efficiency of the solar cell 150.

The second-conduction-type conductive region 30 may have variousstructures other than the above-described structures.

Again referring to FIG. 3, the first passivation film 22 andanti-reflective film 24 are sequentially formed over the front surfaceof the semiconductor substrate 160, in more detail, on thefirst-conduction-type conductive region 20 formed in or on thesemiconductor substrate 160. The first electrode 42 is electricallyconnected to (in more detail, contacts) the first-conduction-typeconductive region 20 through the first passivation film 22 andanti-reflective film 24 (namely, through openings 102).

The first passivation film 22 and anti-reflective film 24 may besubstantially formed throughout the front surface of the semiconductorsubstrate 160, except for the openings 102 corresponding to the firstelectrode 42.

The first passivation film 22 is formed to contact thefirst-conduction-type conductive region 20 and, as such, inactivatesdefects present in the surface or bulk of the first-conduction-typeconductive region 20. Thus, recombination sites of minority carriers areremoved and, as such, open-circuit voltage of the solar cell 150 may beincreased. The anti-reflective film 24 reduces reflectance of lightincident upon the front surface of the semiconductor substrate 160.Thus, the amount of light reaching a pn junction formed by the baseregion 10 and the first-conduction-type conductive region 20 may beincreased in accordance with reduced reflectance of light incident uponthe front surface of the semiconductor substrate 160. Accordingly,short-circuit current Isc of the solar cell 150 may be increased. As aresult, the open-circuit voltage and short-circuit current Isc of thesolar cell 150 may be increased by the first passivation film 22 andanti-reflective film 24 and, as such, the efficiency of the solar cell150 may be enhanced.

The first passivation film 22 may be made of various materials. Forexample, the first passivation film 22 may have a single-layer structureincluding one film selected from the group consisting of a siliconnitride film, a hydrogen-containing silicon nitride film, a siliconoxide film, a silicon oxynitride film, an aluminum oxide film, an MgF₂film, a ZnS film, a TiO₂ film, and a CeO₂ film or may have a multilayerstructure including two or more of the above-listed films incombination. For example, when the first-conduction-type conductiveregion 20 has n-type conductivity, the first passivation film 22 mayinclude a silicon oxide film or silicon nitride film having fixedpositive charges. On the other hand, when the first-conduction-typeconductive region 20 has p-type conductivity, the first passivation film22 may include an aluminum oxide film having fixed negative charges.

The anti-reflective film 24 may be made of various materials. Forexample, the anti-reflective film 24 may have a single-layer structureincluding one film selected from the group consisting of a siliconnitride film, a hydrogen-containing silicon nitride film, a siliconoxide film, a silicon oxynitride film, an aluminum oxide film, an MgF₂film, a ZnS film, a TiO₂ film, and a CeO₂ film or may have a multilayerstructure including two or more of the above-listed films incombination. For example, the anti-reflective film 24 may include asilicon oxide film.

Of course, the embodiments of the present invention are not limited tothe above-described materials, and the first passivation film 22 andanti-reflective film 24 may be made of various materials. One of thefirst passivation film 22 and anti-reflective film 24 may perform boththe anti-reflection function and the passivation function and, as such,the other of the first passivation film 22 and anti-reflective film 24may be omitted. Various films other than the first passivation film 22and anti-reflective film 24 may also be formed on the semiconductorsubstrate 160. In addition, various variations are possible.

The first electrode 42 is electrically connected to thefirst-conduction-type conductive region 20 via the openings 102 formedthrough the first passivation film 22 and anti-reflective film 24 (thatis, through the first passivation film 22 and anti-reflective film 24).The first electrode 42 may be made of a material having excellentelectrical conductivity (for example, metal). The first electrode 42 mayhave a certain pattern to allow transmission of light. A detailedstructure of the first electrode 42 will be described later withreference to FIGS. 9 and 10.

The second passivation film 32 is formed on the back surface of thesemiconductor substrate 160, in more detail, on thesecond-conduction-type conductive region 30 formed at the semiconductorsubstrate 160. The second electrode 44 is electrically connected to (forexample, contacts) the second-conduction-type conductive region 30through the second passivation film 32 (namely, through openings 104).

The second passivation film 32 may be substantially formed throughoutthe back surface of the semiconductor substrate 160, except for theopenings 104 corresponding to the second electrode 44.

The second passivation film 32 is formed to contact thesecond-conduction-type conductive region 30 and, as such, inactivatesdefects present in the surface or bulk of the second-conduction-typeconductive region 30. Thus, recombination sites of minority carriers areremoved and, as such, open-circuit voltage Voc of the solar cell 150 maybe increased.

The second passivation film 32 may be made of various materials. Forexample, the second passivation film may have a single-layer structureincluding one film selected from the group consisting of a siliconnitride film, a hydrogen-containing silicon nitride film, a siliconoxide film, a silicon oxynitride film, an aluminum oxide film, an MgF₂film, a ZnS film, a TiO₂ film, and a CeO₂ film or may have a multilayerstructure including two or more of the above-listed films incombination. For example, when the second-conduction-type conductiveregion 30 has n-type conductivity, the second passivation film 32 mayinclude a silicon oxide film or silicon nitride film having fixedpositive charges. On the other hand, when the second-conduction-typeconductive region 30 has p-type conductivity, the second passivationfilm 32 may include an aluminum oxide film having fixed negativecharges.

Of course, the embodiments of the present invention are not limited tothe above-described materials, and the second passivation film 32 may bemade of various materials. Various films other than the secondpassivation film 32 may also be formed on the back surface of thesemiconductor substrate 160. In addition, various variations arepossible.

The second electrode 44 is electrically connected to thesecond-conduction-type conductive region 30 via the openings 104 formedthrough the second passivation film 32. The second electrode 44 may bemade of a material having excellent electrical conductivity (forexample, metal). The second electrode 44 may have a certain pattern toallow transmission of light. A detailed structure of the secondelectrode 44 will be described later.

As described above, in this embodiment, the first and second electrodes42 and 44 of the solar cell 150 have predetermined patterns and, assuch, the solar cell 150 has a bi-facial structure in which light can beincident upon both the front and back surfaces of the semiconductorsubstrate 160. Accordingly, the amount of light utilized by the solarcell 150 is increased and, as such, an enhancement in efficiency of thesolar cell 150 may be achieved.

Of course, the embodiments of the present invention are not limited tothe above-described structure. The second electrode 44 may have astructure formed throughout the back surface of the semiconductorsubstrate 160. The first and second-conduction-type conductive regions20 and 30 and the first and second electrodes 42 and 44 may also bearranged at one surface of the semiconductor substrate 160 (for example,the back surface). In addition, at least one of the first andsecond-conduction-type conductive regions 20 and 30 may be formed toextend over both surfaces of the semiconductor substrate 160. That is,the above-described solar cell 150 is only illustrative and, as such,the embodiments of the present invention are not limited thereto.

The above-described solar cell 150 is electrically connected to another,neighboring solar cell 150 by leads 142. This will be described in moredetail with reference to FIG. 5 together with FIGS. 1 and 2.

FIG. 5 is a perspective view briefly illustrating a first solar cell 151and a second solar cell 152, which are connected by leads 142, in thesolar cell panel 100 of FIG. 1. In FIG. 5, each solar cell 150 isbriefly illustrated mainly in conjunction with the semiconductorsubstrate 160 and electrodes 42 and 44 thereof. FIG. 6 illustrates onelead 142 before attachment thereof to the electrodes 42 and 44 of onesolar cell 150 illustrated in FIG. 1, through a perspective view and asectional view. FIG. 7 is a sectional view illustrating the lead 142attached to pad sections (designated by reference numeral “422” in FIG.9 or 10) of the electrode 42 or 44 in the solar cell 150 illustrated inFIG. 1. FIG. 8 is a cross-sectional view taken along line VIII-VIII inFIG. 5. In FIG. 7, only the pad sections 422 and lead 142 are shown forsimplicity of illustration and description. In FIG. 8, illustration isgiven mainly in conjunction with leads 142 connecting the first solarcell 151 and the second solar cell 152.

As illustrated in FIG. 5, two neighboring solar cells 150 of a pluralityof solar cells 150 (for example, the first solar cell 151 and secondsolar cell 152) may be connected by leads 142. In this instance, theleads 142 connect the first electrode 42 disposed at the front surfaceof the first solar cell 151 and the second electrode 44 disposed at theback surface of the second solar cell 152 arranged at one side of thefirst solar cell 151 (a left lower side of FIG. 5). Other leads 1420 aconnect the second electrode 44 disposed at the back surface of thefirst solar cell 151 and the first electrode 42 disposed at the frontsurface of another solar cell to be arranged at the other side of thefirst solar cell 151 (a right upper side of FIG. 5). Other leads 1420 bconnect the first electrode 42 disposed at the front surface of thesecond solar cell 152 and the second electrode 44 disposed at the backsurface of another solar cell to be arranged at one side of the secondsolar cell 152 (a left lower side of FIG. 5). Thus, a plurality of solarcells 150 may be connected by the leads 142, 1420 a and 1420 b, to formone solar cell string. In the following description, description givenof leads 142 may be applied to all leads 142 connecting two neighboringsolar cells 150.

In this embodiment, each lead 142 may include a first section 1421connected to the first electrode 42 of the first solar cell 151 (in moredetail, a bus bar line 42 b of the first electrode 42) at the frontsurface of the first solar cell 151 while extending from a first edge161 of the first solar cell 151 toward a second edge 162 of the firstsolar cell 151 opposite the first edge 161, a second section 1422connected to the second electrode 44 of the second solar cell 152 (inmore detail, a bus bar line 44 b of the second electrode 44) at the backsurface of the second solar cell 152 while extending from a first edge161 of the second solar cell 152 toward a second edge 162 of the secondsolar cell 152 opposite the first edge 161 of the second solar cell 152,and a third section 1423 extending from the front surface of the firstsolar cell 151 at the second edge 162 of the first solar cell 151 to theback surface of the second solar cell at the first edge 161 of thesecond solar cell 152, to connect the first section 1421 and secondsection 1422. Accordingly, the lead 142 may be arranged to extend acrossthe first solar cell 151 along a portion of the first solar cell 151while extending across the second solar cell 152 along a portion of thesecond solar cell 152. Since the lead 142 is formed only in regionscorresponding to portions of the first and second solar cells 151 and152 (for example, the bus bar electrodes 42 b) while having a smallerwidth than the first and second solar cells 151 and 152), the lead 142may effectively connect the first and second solar cells 151 and 152 inspite of a small area thereof.

For example, the lead 142 may be arranged at the corresponding first andsecond electrodes 42 and 44 of the first and second solar cells 151 and152, to extend lengthily along the bus bar lines 42 b of the first andsecond electrodes 42 and 44 while contacting the bus bar lines 42 b.Accordingly, the lead 142 continuously contacts the first and secondelectrodes 42 and 44 and, as such, electrical connection characteristicsmay be enhanced. Of course, the embodiments of the present invention arenot limited to the above-described arrangement. The bus bar lines 42 bmay be omitted. In this instance, the leads 142 may be arranged toextend in a direction crossing a plurality of finger lines 42 a, to beconnected to a plurality of finger electrodes 42 a through connectiontherebetween while intersecting the finger lines 42 a. Of course, theembodiments of the present invention are not limited to such anarrangement.

With reference to one surface of each solar cell 150, a plurality ofleads 142 is provided and, as such, electrical connectioncharacteristics of the solar cell 150 to another, neighboring solar cell150 may be enhanced. In particular, in this embodiment, each lead 142 isconstituted by a wire having a smaller width than a ribbon having arelatively great width (for example, 1 to 2 mm), which has been used inconventional instances. To this end, a greater number of leads 142 (forexample, two to five) than that of ribbons as described above are usedwith reference to one surface of each solar cell 150.

As illustrated in FIG. 6, in this embodiment, each lead 142 includes acore layer 142 a, and a coating layer 142 b coated over an outer surfaceof the core layer 142 a to a small thickness. The core layer 142 a isconstituted by a wire having excellent electrical conductivity or thelike, to substantially transfer current. The coating layer 142 b mayhave various functions for protecting the core layer 142 a or enhancingattachment characteristics of the lead 142. For example, the coatinglayer 142 b may include a solder material and, as such, may function toeasily attach the lead 142 to the electrodes 42 and 44 in accordancewith melting thereof by heat. Thus, the lead 142 may be easily attachedto the electrodes 42 and 44 in accordance with soldering throughapplication of heat after the lead 142 is disposed on the electrodes 42and 44, without using a separate adhesive. Accordingly, a tabbingprocess may be simplified.

In this instance, the tabbing process may be carried out by coating aflux over the lead 142, disposing the flux-coated lead 142 on theelectrodes 42 and 44, and then applying heat to the flux-coated lead142. The flux is adapted to prevent formation of an oxide filmobstructing soldering. In this regard, the flux may not be necessary.

The core layer 142 a may include a material exhibiting excellentelectrical conductivity (for example, metal, in more detail, Ni, Cu, Ag,or Al) as a major material thereof (for example, a material having acontent of 50 wt % or more, in more detail, a material having a contentof 90 wt % or more). When the coating layer 142 b includes a soldermaterial, the coating layer 142 b may include a material such as Pb, Sn,SnIn, SnBi, SnPb, SnPbAg, SnCuAg or SnCu as a major material thereof. Ofcourse, the embodiments of the present invention are not limited to theabove-described materials and, the core layer 142 a and coating layer142 b may include various materials.

In another example, the lead 142 may be attached to the electrodes 42and 44, using a separate conductive adhesive. In this instance, the lead142 may or may not include the coating layer 142 b. The conductiveadhesive may be a material constituted by an epoxy-based synthetic resinor silicon-based synthetic resin containing conductive particles of Ni,Al, Ag, Cu, Pb, Sn, SnIn, SnBi, SnP, SnPbAg, SnCuAg, SnCu or the like.The material is maintained in a liquid phase at normal temperature, andis thermally cured by heat applied thereto. When such a conductiveadhesive is used, it may be possible to attach the lead 142 to theelectrodes 42 and 44 by disposing the conductive adhesive on theelectrodes 42 and 44, disposing the lead 142 on the conductive adhesive,and then applying heat to the lead 142, or coating or disposing theconductive adhesive on the surface of the lead 142, disposing the lead142 on the electrodes 42 and 44, and then applying heat to the lead 142.

When the wire, which has a smaller width than the existing ribbon, isused as the lead 142, material costs may be greatly reduced. Since thelead 142 has a smaller width than the ribbon, it may be possible to usea sufficient number of leads 142 and, as such, the movement distance ofcarriers may be minimized. Accordingly, the output power of the solarcell panel 100 may be enhanced.

The wire constituting the lead 142 in accordance with this embodimentmay have a circular or oval cross-section, a curved cross-section, or around cross-section, to induce reflection or diffuse reflection.Accordingly, light reflected from a round surface of the wireconstituting the lead 142 may be reflected or totally reflected upon thefront substrate 110 or back substrate 200 disposed at the front surfaceof back surface of the solar cell 150 and, as such, may be againincident upon the solar cell 150. Thus, the output power of the solarcell panel 100 may be effectively enhanced. Of course, the embodimentsof the present invention are not limited to the above-described shape,and the wire constituting the lead 142 may have a quadrangular shape ora polygonal shape. The wire may also have various other shapes.

In this embodiment, the lead 142 may have a width W1 of 250 to 500 μm.By virtue of the lead 142, which has a wire structure while having theabove-described width, it may be possible to effectively transfercurrent generated in the solar cell 150 to the outside of the solar cell150 or to another solar cell 150. In this embodiment, the lead 142 maybe fixed to the electrodes 42 and 44 of the solar cell 150 after beingindependently disposed on the electrodes 42 and 44 under the conditionthat the lead 142 is not inserted in to a separate layer or film or thelike. Accordingly, when the width W1 of the lead 142 is less than 250μm, the strength of the lead 142 may be insufficient. In addition, thelead 142 may exhibit inferior electrical connection characteristics andlow attachment force because the connection area of the lead 142 to theelectrodes 42 and 44 is too small. On the other hand, when the width W1of the lead 142 is greater than 500 μm, the material costs of the lead142 increase. In addition, the lead 142 may obstruct incidence of lightupon the front surface of the solar cell 150 and, as such, shading lossmay increase. In addition, force applied to the lead 142 in a directionaway from the electrodes 42 and 44 may increase and, as such, attachmentforce between the lead 142 and the electrodes 42 and 44 may be reduced.In severe instances, cracks or the like may be generated at theelectrodes 42 and 44 or the semiconductor substrate 160. For example,the width W1 of the lead 142 may be 350 to 450 μm (in particular, 350 to400 μm). In this range, it may be possible to achieve an enhancement inoutput power while increasing the attachment force to the electrodes 42and 44.

In this instance, the thickness of the coating layer 142 b in the lead142, namely, T2, is as small as 10% or less the width of the core layer142 a before the tabbing process (for example, equal to or less than 20μm, in more detail, 7 to 20 μm). When the thickness T2 of the coatinglayer 142 b is less than 7 μm, it may be impossible to smoothly carryout the tabbing process. On the other hand when the thickness T2 of thecoating layer 142 b is greater than 20 μm, material costs may increase.Furthermore, the strength of the lead 142 may be reduced due to areduction in width of the core layer 142 a. Once the lead 142 isattached to the solar cell 150 in accordance with the tabbing process,the coating layer 142 b flows downwards and, as such, is thicklydeposited between the lead 142 and the solar cell 150 (in more detail,between the lead 142 and the pad sections 422 of the electrodes 42 and44) while being thinly deposited on a surface of the core layer 142 aopposite the solar cell 150, as illustrated in FIG. 7. The portion ofthe coating layer 142 b disposed between the lead 142 and the solar cell150 may have a width W7 equal to or greater than the diameter of thecore layer 142 of the lead 142. The coating layer 142 b may have athickness T1 of 11 to 21 μm at a portion thereof between the lead 142and the pad sections 422 of the electrodes 42 and 44. On the other hand,the coating layer 142 b may have a thickness T2 as small as 2 μm or less(for example, 0.5 to 1.5 μm) at the remaining portion thereof. In thespecification, the width W1 of the lead 142 may mean a width or diameterof the core layer 142 a in a plane perpendicular to a thicknessdirection of the solar cell while passing through a center of the lead142. In this instance, the coating layer 142 b has a very smallthickness at a portion thereof disposed at the center of the core layer142 a and, as such, has little influence on the width of the lead 142.In this regard, the width W1 of the lead 142 may mean a sum of widths ordiameters of the core layer 142 a and coating layer 142 b in the planeperpendicular to the thickness direction of the solar cell while passingthrough the center of the core layer 142 a.

As described above, an enhancement in output power may be achieved bythe provision of the wire-shaped leads 142. In this embodiment, however,neighboring solar cells 150 are electrically connected using leads 142having a smaller width than those of conventional instances and, assuch, the attachment force of the leads 142 to the electrodes 42 and 44may be insufficient because the attachment area of each lead 142 to theelectrodes 42 and 44 may be small. Furthermore, when the leads 142 havea round cross-section having a circular, oval or curved shape, theattachment area of each lead 142 to the electrodes 42 and 44 may befurther reduced and, as such, the attachment force of each lead 142 maybe further reduced. In addition, when the leads 142 have a roundcross-section having a circular, oval or curved shape, the solar cell150 or semiconductor substrate 160 may be more easily bent because thethickness of each lead 142 may be relatively increased.

In particular, in a region between the first solar cell 151 and thesecond solar cell 152, each lead 142 should extend from a position overthe front surface of the first solar cell 151 to a position beneath theback surface of the second solar cell 152. For this reason, the lead 142may be bent in this region. That is, as illustrated in FIG. 8, the firstsection 1421 of the lead 142 is disposed on the first electrode 42 ofthe first solar cell 151 while being maintained in an attached (contact)state to the first electrode 42, and the second section 1422 of the lead142 is disposed on the second electrode 44 of the second solar cell 152while being maintained in an attached (contact) state to the secondelectrode 44. In this instance, the third section 1423 of the lead 142should be connected between the first section 1421 and the secondsection 1422 while preventing the first and second sections 1421 and1422 from being bent. To this end, the third section 1423 may include aportion 1423 a bent to have an arc shape convex toward the front surfaceof the first solar cell 151, so as to be spaced apart from the firstsolar cell 151 by a predetermined distance at the vicinity of the secondedge 162 of the first solar cell 151, and a portion 1423 b bent to havean arc shape convex toward the back surface of the second solar cell152, and connected to the portion 1423 a while having an inflectionpoint with reference to the portion 1423 a, so as to be spaced apartfrom the first solar cell 151 by a predetermined distance at thevicinity of the first edge 161 of the second solar cell 152.

Each of the bent portions 1423 a and 1423 b of the third section 1423has a part extending from a connection point of the third section 1423connected to a corresponding one of the first and second sections 1421and 1422 (namely, a point corresponding to the corresponding edge of thefirst solar cell 151 or second solar cell 152) in a direction away froma corresponding one of the first and second solar cells 151 and 152. Asa result, the lead 142 is subjected to force in a direction away fromthe electrodes 42 and 44 in regions corresponding to facing edges of thesolar cells 150.

As the boundary between the first section 1421 and the third section1423 or the boundary between the second section 1422 and the thirdsection 1423 (namely, a connection point of the lead 142 connected tothe electrode 42 or 44) is closer to the corresponding edge of thecorresponding solar cell 150, the corresponding arc-shaped portion ofthe third section 1423 has a gradually reduced radius of curvature. Inthis instance, force applied to the lead 142 in a direction away fromthe solar cells 150 in regions adjacent to the facing edges of the solarcells 150 is increased and, as such, attachment force of the lead 142 tothe electrodes 42 and 44 may be reduced. For this reason, when thewire-shaped leads 142 are provided, as in this embodiment, ends of theelectrodes 42 and 44 should be spaced apart from the corresponding edgesof the solar cells 150 by a predetermined distance or more in regionscorresponding to respective connection points of each lead 142 and, assuch, the lead 142 may be attached to the electrodes 42 and 44 whilehaving sufficient coupling force or attachment force.

In this embodiment, accordingly, the electrodes 42 and 44 of the solarcells 150 are designed, taking into consideration the above-describedconditions. This will be described in detail with reference to FIGS. 9and 10. Hereinafter, a detailed description will be given in conjunctionwith the first electrode 42 with reference to FIGS. 9 and 10, and thesecond electrode 44 is then described.

FIG. 9 is a plan view illustrating one solar cell included in the solarcell panel of FIG. 1 and leads connected thereto. FIG. 10 is a plan viewillustrating the solar cell included in the solar cell panel of FIG. 1.

Referring to FIGS. 9 and 10, in the illustrated embodiment, the solarcell 150 (or the semiconductor substrate 160) may be divided into anelectrode area EA and an edge area PA. In this instance, the solar cell150 (or the semiconductor substrate 160) may include, for example, firstand second edges 161 and 162 parallel to finger lines 42 a, and thirdand fourth edges 163 and 164 crossing (for example, perpendicularlycrossing or inclinedly crossing) the finger lines 42 a. The third andfourth edges 163 and 164 may include respective central portions 163 aand 164 a occupying large portions of the third and fourth edges 163 and164, and respective inclined portions 163 b and 164 b connected to thefirst and second edges 161 and 162 while extending inclinedly fromrespective central portions 163 a and 164 a. Accordingly, the solar cell150 may have, for example, an almost octagonal shape when viewed in aplane. Of course, the embodiments of the present invention are notlimited to the above-described shape, and the planar shape of the solarcell 150 may be varied.

In this embodiment, the electrode area EA may be an area where thefinger lines 42 a, which extend in parallel, are arranged at a uniformpitch P. The edge area PA may be an area where no finger line 42 a isarranged, or electrode portions are arranged in a lower density thanthat of the finger lines 42 a in the electrode area EA. In thisembodiment, the instance in which the electrode portions of the firstelectrodes 42 are not arranged in the edge area PA is illustrated.

In this embodiment, the electrode area EA may include a plurality ofelectrode areas divided with reference to the bus bar lines 42 b orleads 142. In more detail, the electrode area EA may include a firstelectrode area EA1 defined between two neighboring bus bar lines 42 b orleads 142, and two second electrode areas EA2 each defined between acorresponding one of the third and fourth edges 163 and 164 in the solarcell 150 and the lead 142 arranged adjacent thereto. In this embodiment,since a plurality of leads 142 (for example, six or more) is providedwith reference to one surface of the solar cell 150, a plurality offirst electrode areas EA1 may be provided (the number of first electrodeareas EA1 being smaller than the number of leads 142 by one).

In this instance, the width of each first electrode area EA1, namely, awidth W2, may be smaller than the width of each second electrode areaEA2, namely, a width W3. In this embodiment, a number of leads 142 orbus bar lines 42 b are provided. Accordingly, the width W3 of eachsecond electrode area EA2 should be relatively great in order to allowthe inclined portions 163 b or 164 b of the third or fourth edge 163 or164 to be disposed in the second electrode area EA2 and, as such, it maybe possible to prevent the bus bar lines 42 b or leads 142 from beingdisposed at the third or fourth edge 163 or 164. Of course, theembodiments of the present invention are not limited to theabove-described conditions, and the width W2 of each first electrodearea EA1 and the width W3 of each second electrode area EA2 may havevarious values.

In this embodiment, since the bus bar lines 42 b and leads 142 arearranged at a uniform pitch, the widths W2 of the first electrode areasEA1 may be substantially equal. Accordingly, carriers may migrate for auniform average movement distance and, as such, carrier collectionefficiency may be enhanced.

Meanwhile, the edge area PA may include first edge areas PA1 eachcorresponding to a region where each lead 142 is disposed, while beingdefined between neighboring finger lines 42 a, and second edge areas PA2corresponding to a remaining portion of the edge area PA, except for thefirst edge areas PA1, while being defined between outermost ones of thefinger lines 42 a and corresponding ones of the first to fourth edges161, 162, 163 and 164 of the semiconductor substrate 160, to provide apredetermined distance between the semiconductor substrate 160 and thefirst electrode 42. Each edge area PA1 may be arranged at a regionportion adjacent to the corresponding edge of the solar cell 150 in thecorresponding region where one lead 142 is disposed. Each first edgearea PA1 is an area where each end of the first electrode 42 is spacedapart from the corresponding edge of the solar cell 150, to allow thecorresponding lead 142 to be attached to the first electrode bysufficient coupling force.

The first electrode 42 may include a plurality of finger lines 42 aspaced apart from one another in the electrode area EA while having auniform width W5 and a uniform pitch P. In FIG. 9, the finger lines 42 aare illustrated as being parallel while being parallel to the main edgesof the solar cell 150 (in particular, the first and second edges). Ofcourse, the embodiments of the present invention are not limited to theabove-described arrangement.

For example, the finger lines 42 a of the first electrode 42 may have awidth W5 of 35 to 120 μm. The finger lines 42 a of the first electrode42 may also have a pitch P of 1.2 to 2.8 mm. The number of finger lines42 a arranged in a direction crossing the finger lines 42 a may be 55 to130. The above-described width W5 and pitch P may be obtained undersimple process conditions. The width W5 and pitch P are defined tominimize shading loss caused by the finger lines 42 a while achievingeffective collection of current produced through photoelectricconversion. Each finger line 42 a may have a thickness of 5 to 50 μm.Such a thickness of the finger line 42 a may be easily obtained in aprocess of forming the finger line 42 a. In addition, the finger line 42a may have desired specific resistance in the above-described thicknessrange. Of course, the embodiments of the present invention are notlimited to the above-described conditions and, the width, pitch,thickness, etc., of the finger lines 42 a may be varied in accordancewith variation of process conditions, the size of the solar cell 150,the material of the finger lines 42 a, or the like.

In this instance, the width W1 of the leads 142 may be smaller than thepitch P of the finger lines 42 a while being greater than the width ofthe finger lines 42 a. Of course, the embodiments of the presentinvention are not limited to such conditions, and various variations arepossible.

In addition, the first electrode 42 may include bus bar lines 42 bformed in a direction crossing the finger lines 42 a in the electrodearea EA, to connect the finger lines 42 a. For example, each bus barline 42 b may be formed to extend continuously from a region adjacent tothe first edge 161 to a region adjacent to the second edge 162. Asdescribed above, each bus bar line 42 b may be disposed to correspond toa region where each lead 142 is disposed to connect neighboring solarcells 150. The bus bar lines 42 b may be provided to correspond to theleads 142 one to one. In this embodiment, accordingly, the bus bar lines42 b are equal in number to the leads 142 with reference to one surfaceof the solar cell 150. In this embodiment, each bus bar line 42 b maymean an electrode portion disposed adjacent to the corresponding lead142, and is formed to extend in a direction perpendicularly orinclinedly crossing the finger lines 42 a while being connected to orcontacting the corresponding lead 142.

Each bus bar line 42 b may include a line section 421 extendinglengthily in a direction that the corresponding lead 142 is connected tothe bus bar line 42 b, while having a relatively small width, and padsections 422 having a greater width than the line section 421, toincrease a connection area to the corresponding lead 142. By virtue ofthe narrow line section 421, it may be possible to minimize the areablocking light incident upon the solar cell 150. By virtue of the widepad sections 422, it may be possible to enhance attachment force betweenthe lead 142 and the bus bar line 42 b while reducing contactresistance. Each bus bar line 42 b may include extension sectionsconnected to ends of the finger lines 42 a adjacent to a correspondingone of the first edge areas PA1 while dividing the corresponding firstedge area PA1 from the electrode area EA.

The pad sections 422 may include first pad sections 422 a disposed atopposite ends of the line section 421 (namely, regions where the lead142 is connected to the first electrode 42), and second pad sections 422b disposed in an inside region of the bus bar line 42 b, except for thefirst pad sections 422 a. As described above, force may be applied tothe lead 142 at the ends of the line section 421 or at the first padsections 422 a in a direction away from the first electrode 42 (adirection away from the semiconductor substrate 160). Accordingly, whenthe first pad sections 422 a have a greater area than the second padsections 422 a, strong attachment force may be provided between the lead142 and the first electrode 42. In this instance, even when the firstpad sections 422 a have a greater width than the second pad sections 422b, there is no remarkable effect in enhancing attachment force to thelead 142. In this regard, the first pad sections 422 a may have a lengthL1 (a length measured in a longitudinal direction of the lead 142)greater than a length L2 of the second pad sections 422 b (a lengthmeasured in the longitudinal direction of the lead 142).

The pad sections 422 may have a width (in more detail, the widths of thefirst pad sections 422 a and second pad sections 422 b) greater thanthose of the line section 421 and finger lines 42 a. The pitch of thebus bar lines 42 b may be greater than the pitch of the finger lines 42a.

In this embodiment, the line sections 421 of the bus bar lines 42 b areillustrated as corresponding to respective leads 142. In more detail, inconventional instances, bus bar electrodes, which correspond to theleads 142 and have a much greater width than the finger lines 42 a, areprovided. In this embodiment, however, the line sections 421 of the busbar lines 42 b, which have a much smaller width than the bus barelectrodes, are provided. In this embodiment, each line section 421connects a plurality of finger lines 42 a and, as such, provides a path,along which bypass of carriers is carried out when a part of the fingerlines 42 a is short-circuited.

In the specification, the bus bar electrodes mean electrode portionsformed in a direction crossing the finger lines, to correspond torespective ribbons, while having a width corresponding to 12 times ormore (normally 15 times or more) the width of each finger line. Sincethe bus bar electrodes have a relatively great width, two or three busbar electrodes are formed at normal instances. Meanwhile, the linesections 421 of the bus bar lines 42 b in this embodiment may meanelectrode portions formed in a direction crossing the finger lines 42 a,to correspond to respective leads 142, while having a widthcorresponding to 10 times or less the width of each finger line 42 a.

For example, the width of the line section 421, namely, a width W4, maybe 0.5 to 10 times the width of each finger line 42 a, namely, a widthW5. When the ratio of the width W4 to the width W5 is 0.5 or less,effects of the line section 421 may be insufficient. On the other hand,when the ratio is greater than 10, shading loss may be increased becausethe width W4 of the line section 421 is excessively great. Inparticular, in this embodiment, a number of line sections 421 isprovided because a number of leads 142 is provided and, as such, shadingloss may be further increased. In more detail, the width W4 of the linesection 421 may be 0.5 to 7 times the width W5 of the finger line 42 a.For example, the width W4 of the line section 421 may be 0.5 to 4 timesthe width W5 of the finger line 42 a, taking shading loss intoconsideration. In more detail, the width W4 of the line section 421 maybe 0.5 to 3 times the width W5 of the finger line 42 a. In this range,efficiency of the solar cell 150 may be greatly enhanced.

Meanwhile, the width W4 of the line section 421 may be equal to orsmaller than the width W1 of the lead 142. When the lead 142 has acircular, oval or round shape, the contact width or area of the lead 142contacting the line section 421 at a back surface thereof and, as such,the width W4 of the line section 421 may be equal to or smaller than thewidth W1 of the lead 142. When the width W4 of the line section 421 isrelatively small, it may be possible to reduce the material costs of thefirst electrode 42 through reduction of the area of the first electrode42.

For example, the ratio of the width W1 of the lead 142 to the width W4of the line section 421 may be 1:0.07 to 1:1. When the ratio is lessthan 1:0.07, electrical characteristics or the like may be degradedbecause the width W4 of the line section 421 is too small. On the otherhand, when the ratio is greater than 1:1, it may be impossible togreatly enhance contact characteristics to the line section 421 or thelike in spite of an increase in area of the first electrode 42. As aresult, shading loss, material costs, etc., may be increased. Forexample, the ratio may be 1:0.1 to 1:0.5 (in more detail, 1:0.1 to1:0.3), taking into consideration shading loss, material costs, etc.

Meanwhile, the width W4 of the line section 421 may be 35 to 350 μm.When the width W4 of the line section 421 is less than 35 μm, electricalcharacteristics or the like may be degraded because the width W4 of theline section 421 is too small. On the other hand, when the width W4 ofthe line section 421 is greater than 350 μm, it may be impossible togreatly enhance contact characteristics to the line section 421 or thelike in spite of an increase in area of the first electrode 42. As aresult, shading loss, material costs, etc., may be increased. Forexample, the width W4 of the line section 421 may be 35 to 200 μm (inmore detail, 35 to 120 μm), taking into consideration shading loss,material costs, etc.

Of course, the embodiments of the present invention are not limited tothe above-described conditions and, the width W4 of the line section 421may be varied within a range capable of minimizing shading loss whileeffectively transferring current produced through photoelectricconversion.

Meanwhile, the width of each pad section 422, namely, a width W6, isgreater than the width W4 of the line section 421 while being equal toor greater than the width W1 of the lead 142. Since the pad section 422is a section to achieve an enhancement in attachment force of the lead142 through increase of a contact area thereof to the lead 142, the padsection 422 has a width greater than the width of the line section 421while being equal to or greater than the width of the lead 142.

For example, the ratio of the width W1 of the lead 142 to the width W6of the pad section 422 may be 1:1 to 1:5. When the ratio is less than1:1, attachment force between the pad section 422 and the lead 142 maybe insufficient because the width W6 of the pad section 422 isinsufficient. On the other hand, when the ratio is greater than 1:5,shading loss may be increased because the area of the pad section 422causing shading loss is increased. The ratio may be 1:2 to 1:4 (in moredetail, 1:2.5 to 1:4), taking into consideration attachment force,shading loss, etc.

Meanwhile, for example, the width W6 of the pad section 422 may be 0.25to 2.5 mm. When the width W6 of the pad section 422 is less than 0.25mm, attachment force between the pad section 422 and the lead 142 may beinsufficient because the contact area of the pad section 422 to the lead142 is insufficient. On the other hand, when the width W6 of the padsection 422 is greater than 2.5 mm, shading loss may be increasedbecause the area of the pad section 422 causing shading loss isincreased. For example, the width W6 of the pad section 422 may be 0.8to 1.5 mm.

Meanwhile, the pad section 422 may have lengths L1 and L2 greater thanthe width of each finger line 42 a. For example, the lengths L1 and L2of the pad section 422 may be 0.035 to 30 mm. When the lengths L1 and L2of the pad section 422 are less than 0.035 mm, attachment force betweenthe pad section 422 and the lead 142 may be insufficient because thecontact area of the pad section 422 to the lead 142 is insufficient. Onthe other hand, when the lengths L1 and L2 of the pad section 422 aregreater than 30 mm, shading loss may be increased because the area ofthe pad section 422 causing shading loss is increased.

In this instance, the length L1 of each first pad section 422 a, towhich greater force is applied, may be greater than the length L2 ofeach second pad section 422 b. In more detail, the length L1 of thefirst pad section 422 a may be 0.4 to 30 mm. Taking shading loss intoconsideration, the length L1 of the first pad section 422 a may be 0.4to 3.2 mm. The length L2 of each second pad section 422 b may be 0.035to 1 mm. In more detail, the length L2 of the second pad section 422 bmay be 0.4 to 1 mm. Accordingly, attachment force obtained by the firstpad section 422 a, to which greater force is applied, may be furtherincreased, and the area of the second pad section 422 b may be reducedand, as such, shading loss, material costs, etc., may be reduced. Ofcourse, the embodiments of the present invention are not limited to theabove-described conditions and, the width of the first pad section 422 amay be greater than the width of the second pad section 422 b.Alternatively, the width and length of the first pad section 422 a maybe greater than those of the second pad section 422 b, respectively.

Meanwhile, for example, the ratio of the width W5 of each finger line 42a to the lengths L1 and L2 of the pad section 422 may be 1:1.1 to 1:20.Within this range, the attachment area between the pad section 422 andthe lead 142 is increased and, as such, attachment force between the padsection 422 and the lead 142 may be increased.

Meanwhile, for example, the ratio of the width W1 of the lead 142 to thelengths L1 and L2 of each pad section 422 may be 1:1 to 1:10. When theratio is 1:1, attachment force between the pad section 422 and the lead142 may be insufficient because the lengths L1 and L2 of the pad section422 are insufficient. On the other hand, when the ratio is greater than1:10, shading loss may be increased because the area of the pad section422 causing shading loss is increased. The ratio may be 1:3 to 1:6,taking into consideration attachment force, shading loss, etc.

For one bus bar line 42 b, 6 to 24 (for example, 12 to 22) pad sections422 may be provided. The pad sections 422 may be arranged while beingspaced apart from one another by a certain distance. For example, onepad section 422 may be arranged per 2 to 10 finger lines 42 a. Inaccordance with this arrangement, regions where the contact area betweenthe bus bar line 42 b and the lead 142 increases are regularly providedand, as such, attachment force between the bus bar line 42 b and thelead 142 may be increased. Alternatively, the pad sections 422 may bearranged such that the distance between adjacent ones of the padsections 422 is varied. In particular, the pad sections 422 may bearranged in a higher density at end portions of the bus bar line 42 b,to which greater force is applied, as compared to the remaining portionof the bus bar line (namely, the central portion of the bus bar line 42b). Of course, various variations are possible.

Again referring to FIG. 7, when a coating layer 142 b (a separatecoating layer for attachment of the lead 142 to the pad sections 422,for example, a soldering layer) is disposed in a region adjacent to eachpad section 422, the ratio of the width W1 of the lead 142 to the widthof the coating layer 142 b, namely, a width W7, may be 1:1 to 1:3.33. Ofcourse, the embodiments of the present invention are not limited to theabove-described conditions, and the ratio may have various values.

Meanwhile, the width of each pad section 422 may be equal to or greaterthan the width W7 of the coating layer 142 b in the region adjacent toeach pad section 422. For example, the width W7 of the coating layer 142b in the region adjacent to the pad section 422 to the width W6 of thepad section 422 may be 1:1 to 1:4.5. When the ratio is less than 1:1,bonding characteristics of the lead 142 and pad section 422 may beinferior. On the other hand, when the ratio is greater than 1:4.5,shading loss and manufacturing costs may increase because the area ofthe pad section 422 increases.

Of course, the embodiments of the present invention are not limited tothe above-described conditions and, the width W6 and lengths L1 and L2of each pad section 422 may have various values within a range capableof enhancing attachment force of the pad section 422 to the lead 142through an increase in contact area of the pad section 422 to the lead142. Alternatively, it may be possible to separately provide the padsections 422.

Again referring to FIG. 9, each bus bar line 42 b may include extensionsections 423 connected to each end of the line section 421 in the busbar line 42 b while dividing the corresponding first edge area PA1 fromthe corresponding electrode area EA. The extension sections 423 mayconnect ends of the finger lines 42 a disposed adjacent to the firstedge area PA1. When the extension sections 423 are provided, theextension sections 423 function to provide a path, along which carriersmay flow when a part of the finger lines 42 a is short-circuited.

The extension sections 423 may be inclinedly disposed on the fingerlines 42 a and bus bar line 42 b such that the width of the first edgearea PA1 is gradually increased toward a corresponding one of the firstand second edges 161 and 162 of the solar cell 150. For example, thefirst edge area PA1 may have an almost triangular shape. The twoextension sections 423 defining the first edge area PA1 may form analmost “V” shape. In accordance with such shapes, facing outer ends ofthe finger lines 42 a in two electrode areas EA adjacent to the firstedge area PA1 may be arranged to be gradually spaced farther apart fromeach other. In addition, the first edge area PA1 may have a shape with awidth gradually increasing toward the corresponding first or second edge161 or 162 of the solar cell 150 between the two electrode areas EA.Accordingly, the end portion of each electrode area EA adjacent to thefirst edge area PA1 may have a smaller width than the remaining portionof the electrode area EA. For example, the first edge area PA1 may havean isosceles triangle shape, and each electrode area EA may have analmost octagonal shape.

Accordingly, each lead 142 may be stably disposed in the correspondingedge areas PA1 without being attached to the corresponding extensionsections 423. In this embodiment, one end of each lead 142 (an upper endin FIG. 9) not connected to another solar cell 150 may extend to theinside of the corresponding first edge area PA1 arranged between one endof the corresponding line section 421 and the corresponding edge of thesolar cell 150 (namely, the first edge 161) after passing one end of theline section 421 (an upper end in FIG. 9) and, as such, may be disposedinside the first edge area PAL Accordingly, it may be possible to stablyfix the lead 142 to one end of the line section 421 and, as such, thelead 142 may be fixed to the first electrode 42 by sufficient attachmentforce. On the other hand, when one end of the lead 142 is disposed atthe end of the line section 421, or does not reach the end of the linesection 421, the end of the lead 142 may be unstably attached to thefirst pad section 422 a disposed at the end of the line section 421.Meanwhile, when the lead 142 extends to the corresponding second edgearea PA2, unnecessary short-circuit may be generated.

Meanwhile, the other end of the lead (a lower end in FIG. 9) isconnected to the bus bar line 42 b of the neighboring solar cell 150after passing the other end of the line section 421, the correspondingedge area PA1 and the corresponding second edge area PA.

For example, the length of a portion of the lead 142 disposed in eachfirst edge area PA1 may be greater than the length of a portion of thefirst edge area PA1 where the portion of the lead 142 is not disposed.That is, the ratio of a length L3 of the first edge area PA1 to a lengthL4 of the first edge area PA1 may be 1:0.5 to 1:1. In this instance, thelead 142 may be stably attached to the first pad section 422 a. In moredetail, the ratio of the length L3 of the first edge area PA1 to thelength L4 of the first edge area PA1 may be 1:0.6 to 1:0.9. Within thisrange, the lead 142 may be stably attached to the first pad section 422a while being prevented from extending to the corresponding second edgearea PA2. Of course, the embodiments of the present invention are notlimited to the above-described conditions.

Meanwhile, the lead 142 may be disposed without being attached to thesolar cell 150 in the first edge area PA1 under the condition that thelead 142 is attached to the bus bar line 42 b. This is because thecoating layer 142 b of the lead 142, which includes a solder material,may be hardly attached to the solder cell 150 in a region where the busbar line 42 b is not disposed, even though the coating layer 412 b maybe securely attached to the bus bar line 42 b (in particular, the padsections 422).

The width of each first edge area PA1 disposed between outermost ones ofthe corresponding finger lines 42 a, namely, a width W8, may be greaterthan the width of the lead 142. Accordingly, the lead 142 may be stablydisposed in the first edge area PA1. In particular, the lead 142 may bemaintained in the first edge area PA1 even when the lead 142 islaterally bent within the first edge area PA1 during a process ofattaching the lead 142.

The width W8 of the first edge area PA1 may be 0.73 to 3.8 mm. Forexample, the width W8 of the first edge area PA1 may be 0.73 to 2 mm.Meanwhile, the ratio of the width W1 of the lead 142 to the width of thefirst edge area PA1 may be 1:1.46 to 1:15.2 (for example, 1:1.46 to1:5). Within this range, the lead 142 may be stably disposed in thefirst edge area PA1.

Meanwhile, assuming that “L” represents the width W8 of the first edgearea PA1, and “D” represents an edge distance, “L” and “D” may satisfythe following Expression 1. Here, the edge distance D means the distancebetween each end of the first electrode 42 and the edge of the solarcell 150 adjacent to the end of the first electrode 42 (in more detail,the first or second edge 161 or 162) in a region where the lead 142 isdisposed.0.9*(0.1569*D+0.3582)≤L≤1.1*(0.1569*D+0.3582)  <Expression 1>

(Here, the unit of “L” is mm, and the unit of “D” is mm.)

The above Expression 1 is based on the fact that the width W9 of thefirst edge area PA1 should be sufficiently great when the edge distanceD is great, because a phenomenon in which the lead 142 is bent mayincrease when the edge distance D increases. Of course, the embodimentsof the present invention are not limited to the above-describedconditions.

The width of each extension section 423 is smaller than the width of theline section 421. For example, the width of the line section 421 mayhave a value corresponding to 2 times or more the width of eachextension section 423. Then, the sum of the widths of two extensionsections 423 in a region where the two extension sections 423 arebranched from the line section 421 is equal to or smaller than the widthof the line section 421. Accordingly, it may be possible to minimize thewidth of each extension section 423 while preventing the width of thebus bar line 42 b from being increased in a region where the twoextension sections 423 are connected to the line section 421. Forexample, the width W4 of the line section 421 may be 2 to 10 times thewidth of each extension sections 423. Meanwhile, for example, the linewidth of each extension section 423 may be 35 to 120 μm.

Meanwhile, the width of each extension section 423 may be equal orsimilar to the width of each finger line 42 a. For example, the width ofeach extension section 423 may be 2 times or less (for example, 0.5 to 2times) the width of each finger line 42 a. In this instance, it may bepossible to avoid an increase in shading loss caused by the extensionsections 423 while achieving effects of the extension sections 423. Ofcourse, the embodiments of the present invention are not limited to theabove-described conditions and, each extension section 423 may havevarious widths in a range capable of connecting the corresponding fingerlines 42 a, thereby achieving flow of current.

In this embodiment, each bus bar line 42 b may have a thickness of 3 to45 μm. Within this thickness range, the bus bar line 42 b may be easilyformed, and may have a desired specific resistance. Of course, theembodiments of the present invention are not limited to theabove-described conditions and, the thickness of the bus bar line 42 bor the like may be varied in accordance with variations of processconditions, size of the solar cell 150, the material of the bus bar line42 b, etc.

In this embodiment, the finger lines 42 a and the bus bar lines 42 b maybe formed as different layers, respectively. For example, as illustratedin an enlarged upper circle of FIG. 9, the bus bar lines 42 b are firstformed, and the finger lines 42 a are then formed to be disposed overthe bus bar lines 42 b such that the finger lines 42 a corresponding toeach bus bar lines 42 b overlap at least a portion of the correspondingbus bar line 42 b. In this embodiment, the finger lines 42 a disposed atone side (for example, a left side of FIG. 9) of each bus bar line 42 band the finger lines 42 a disposed at the other side (for example, aright side of FIG. 9) of the bus bar line 42 b are spaced apart fromeach other. On the bus bar line 42 b, accordingly, there is a regionwhere no finger line 42 a is formed and, as such, manufacturing costsmay be minimized in association with formation of the finger lines 42 a.Of course, the embodiments of the present invention are not limited tothe above-described conditions and, the finger lines 42 a may bedisposed to cross the entire portion of the bus bar line 42 b.

The finger lines 42 a and the bus bar lines 42 b may be made of the samematerial or different materials. For example, when the finger lines 42 aand bus bar lines 42 b are formed by printing, a paste for forming thebus bar lines may have relatively low viscosity, whereas a paste forforming the finger lines 42 a may have relatively high viscosity. Inthis instance, accordingly, after curing, the bus bar lines have agreater thickness than the finger lines 42 a. In this regard, when thefinger lines 42 a are formed after formation of the bus bar lines 42 b,as described above, more stable formation thereof may be achieved.

For example, the paste for forming the finger lines 42 a may have agreater content of metal (for example, silver) than the paste forforming the bus bar lines 42 b. In this instance, the resistance of thefinger lines 42 a directly associated with collection of carriers may bereduced and, as such, an enhancement in carrier collection efficiencymay be achieved. In addition, a reduction in manufacturing costs may beachieved in accordance with a reduction in metal content of the bus barlines 42 b.

Meanwhile, the finger lines 42 a of the first electrode 42 may be formedto extend through the passivation film 22 and anti-reflective film 24,and the bus bar lines 42 b may be formed on the passivation film 22 andanti-reflective film 24. In this instance, openings (designated byreference numeral “102” in FIG. 3) having a shape corresponding to thefinger lines 42 a may be formed in regions where no bus bar line 42 b isformed. That is, the openings are not formed in regions where the busbar lines 42 b are formed. In this instance, the first-conduction-typeconductive region 20 may have a shape corresponding to regions where theopenings 102 are formed. That is, in the electrode area EA, thefirst-conduction-type conductive region 20 may be formed to have a shapecorresponding to the finger lines 42 a, without being formed in regionscorresponding to the bus bar lines 42 b. In this instance, the linesection 421, pad sections 422 and extension sections 423 constitutingeach bus bar line 42 b are formed on the passivation film 22 andanti-reflective film 24, and the first-conduction-type conductive region20 may be not formed in regions corresponding to the sections 421, 422and 423 of each bus bar line 42 b. Then, the line section 421, padsections 422 and extension sections 423 of each bus bar line 42 b mayconstitute a floating electrode.

Of course, the embodiments of the present invention are not limited tothe above-described conditions and, the bus bar lines 42 b may be formedafter formation of the finger lines 42 a. Alternatively, the fingerlines 42 a and the bar lines 42 b may be simultaneously formed through asingle process, using the same material, and, as such, may take the formof a single layer. Other variations are possible.

Meanwhile, the first electrode 42 may further include edge lines 42 ceach connected to ends of the outermost finger lines 42 a adjacent to acorresponding one of the third and fourth edges 163 and 164 whiledividing a corresponding one of the second edge areas PA2 from theelectrode area EA. Each edge line 42 c may be spaced apart from thecorresponding third or fourth edge 163 or 164 by a uniform distance in aregion adjacent to the corresponding third or fourth edge 163 or 164while having a shape identical or similar to that of the correspondingthird or fourth edge 163 or 164. In this instance, each edge line 42 cconnects the ends of the finger lines 42 a adjacent to the correspondingthird or fourth edge 163 or 164.

The second edge areas PA2 may be arranged between the edge lines 42 cand the third and fourth edges 163 and 164 and between the first andsecond edges 161 and 162 and the outermost finger lines 42 a adjacent tothe first and second edges 161 and 162, respectively, to take the formof a frame. Each second edge area PA2 may have a width W9 of 0.5 to 1.5mm. When the width W9 of the second edge area PA2 is less than 0.5 mm,unnecessary shunting may occur. On the other hand, when the width W9 ofthe second edge area PA2 is greater than 1.5 mm, the area of anineffective region may increase and, as such, efficiency of the solarcell 150 may be insufficient. Of course, the embodiments of the presentinvention are not limited to the above-described conditions.

The width of each edge line 42 c may be equal or similar to the width ofeach finger line 42 a. The width and thickness of each finger line 42 aand relations of each finger line 42 a with other electrode sections andthe lead 142 may be applied to the edge lines 42 c in the same manner.

In this embodiment, when “W” represents the width W1 of the lead 142,and “D” represents the edge distance between each end of the firstelectrode 42 and the edge of the solar cell 150 adjacent to the end ofthe first electrode 42 (in more detail, the first or second edge 161 or162) in a region where the lead 142 is disposed, “W” and “D” may satisfythe following Expression 2.13.732*ln(W)−71.436−0.0000321462*(W)²≤D≤13.732*ln(W)−71.436+0.0000321462*(W)²  <Expression 2>

(Here, the unit of “W” is μm, and the unit of “D” is mm.)

As described above, force is applied, in a direction away from the solarcell 150, to the lead 142 at an end of the first electrode where thelead 142 is disposed and, as such, attachment force between the lead 142and the first electrode 42 may be reduced. That is, as illustrated inFIG. 11, when the width W1 of the lead 142 increases, the bending degreeof the solar cell 150 or semiconductor substrate 160 is increased. Forreference, in FIG. 11, “300 Wire” corresponds to the instance in whichthe width W1 of the lead 142 is 300 μm, “330 Wire” corresponds to theinstance in which the width W1 of the lead 142 is 330 μm, and “400 Wire”corresponds to the instance in which the width W1 of the lead 142 is 400μm. When the width W1 of the lead 142 increases, greater force isapplied to the lead 142 at an end of the first electrode in a directionaway from the solar cell 150 and, as such, attachment force between thelead 142 and the first electrode 42 may be reduced. In order to preventsuch attachment force reduction, the edge distance D is sufficientlysecured in this embodiment, to minimize stress applied to the firstelectrode 42.

That is, when the width W1 of the lead 142 increases, it may be possibleto provide sufficient attachment force between the lead 142 and thefirst electrode 42 by increasing the edge distance D, and then proposedthe range of the edge distance D according to the width W1 of the lead142 as expressed in Expression 2.

In more detail, the attachment force of the lead 1422 at the end of thefirst electrode 42 is measured while varying the width W1 of the lead142 and the edge distance D. During measurement, instances in whichattachment force having a predetermined value or more (for example, 1.5Nor more, more preferably, 2N or more) is exhibited were sought, andinstances having the predetermined value or more were marked in FIG. 12,using a mark “x”. Thereafter, a range of the edge distance D accordingto the width W1 of the lead 142 where marks “x” are located was soughtand, as such, the above Expression 2 as to lower and upper limits of theedge distance D was derived.

When the edge distance D is within the range expressed by the aboveExpression 2 under the condition that the width W1 of the lead 142 has aconstant value, the lead 142, which has a wire shape, may be maintainedin a state of being stably attached to the ends of the first electrode42. In this embodiment, accordingly, it may be possible not only toachieve various effects according to use of the lead 142, which has awire shape, but also to enhance the attachment force of the lead 142through adjustment of the edge distance D.

Since the width W1 of the lead 142 is 250 to 500 μm, the edge distance Dmay have a value of 2.37 to 21.94 mm. In more detail, when the width W1of the lead 142 is equal to or greater than 250 μm, but less than 300μm, the edge distance D may be 2.37 to 9.78 mm. When the width W1 of thelead 142 is equal to or greater than 300 μm, but less than 350 μm, theedge distance D may be 3.99 to 12.94 mm. When the width W1 of the lead142 is equal to or greater than 350 μm, but less than 400 μm, the edgedistance D may be 5.06 to 15.98 mm. When the width W1 of the lead 142 isequal to or greater than 400 μm, but less than 450 μm, the edge distanceD may be 5.69 to 18.96 mm. When the width W1 of the lead 142 is equal toor greater than 450 μm, but less than 500 μm, the edge distance D may be5.94 to 21.94 mm. In the above-described ranges, Expression 2 issatisfied and, as such, superior attachment force may be provided.

For example, when the width W1 of the lead 142 is equal to or greaterthan 250 μm, but less than 300 μm, the edge distance D may be 4 to 9.78mm. When the width W1 of the lead 142 is equal to or greater than 300μm, but less than 350 μm, the edge distance D may be 6 to 12.94 mm. Whenthe width W1 of the lead 142 is equal to or greater than 350 μm, butless than 400 μm, the edge distance D may be 9 to 15.98 mm. When thewidth W1 of the lead 142 is equal to or greater than 400 μm, but lessthan 450 μm, the edge distance D may be 10 to 18.96 mm. When the widthW1 of the lead 142 is equal to or greater than 450 μm, but less than 500μm, the edge distance D may be 12 to 21.94 mm. In the above-describedranges, sufficient attachment force may be more stably provided. Inparticular, in this embodiment, when the width W1 of the lead 142 isequal to or greater than 350 μm, but less than 400 μm, the edge distanceD may be 9 to 15.98 mm. In this instance, the output power of the solarcell panel 100 may be maximized. Of course, the embodiments of thepresent invention are not limited to the above-described conditions.

For example, the edge distance D may be smaller than the width W2 of thefirst electrode area EA1 (namely, the distance or pitch between twoneighboring bus bar lines 42 b or between neighboring leads 142 whilebeing smaller than the width W3 of the second electrode area EA2(namely, the distance between the bus bar line 42 b or lead 142 adjacentto an edge of the solar cell 150 and the edge of the solar cell 150).Accordingly, the edge distance D may be defined to achieve anenhancement in carrier collection efficiency. Of course, the embodimentsof the present invention are not limited to the above-describedconditions.

In this embodiment, the edge distance D between each first pad section422 a and a corresponding one of the first and second edges 161 and 162may satisfy the above Expression 2 because the first pad section 422 ais arranged at the corresponding end of the bus bar line 42 b where thelead 142 is disposed.

The number of leads 142 (the number of bus bar lines 42 b) arranged atone surface of the solar cell 150 relates to the width W1 of each lead142. FIG. 13 is a diagram depicting outputs of the solar cell panel 100measured while varying the width of each lead 142 and the number ofleads 142. Referring to FIG. 13, it may be found that, when 6 to 33leads 142 having a width W1 of 250 to 500 μm are provided, the outputpower of the solar cell panel 100 exhibits a superior value. In thisinstance, it may be found that, when the width W1 of each lead 142increases, the required number of leads 142 may be reduced.

For example, when the width W1 of the lead 142 is equal to or greaterthan 250 μm, but less than 300 μm, the number of leads 142 (withreference to one surface of the solar cell 150) may be 15 to 33. Whenthe width W1 of the lead 142 is equal to or greater than 300 μm, butless than 350 μm, the number of leads 142 may be 10 to 33. When thewidth W1 of the lead 142 is equal to or greater than 350 μm, but lessthan 400 μm, the number of leads 142 may be 8 to 33. When the width W1of the lead 142 is equal to or greater than 400 μm, but less than 500μm, the number of leads 142 may be 6 to 33. Meanwhile, when the width W1of the lead 142 is equal to or greater than 350 μm, it may be difficultto further increase the output power of the solar cell panel 100 eventhough the number of leads 142 exceeds 15. When the number of leads 142increases, load on the solar cell 150 may be increased. In this regard,when the width W1 of the lead 142 is equal to or greater than 350 μm,but less than 400 μm, the number of leads 142 may be 8 to 15. Inaddition, when the width W1 of the lead 142 is equal to or greater than400 μm, but less than 500 μm, the number of leads 142 may be 6 to 15. Inorder to further enhance the output power of the solar cell panel 100,the number of leads 142 may be equal to or greater than 10 (for example,12 to 13). Of course, the embodiments of the present invention are notlimited to the above-described conditions and, the number of leads 142and the number of bus bar lines 42 b may have various values.

Meanwhile, the pitch of leads 142 (or the pitch of bus bar lines 42 b)may be 4.75 to 26.13 mm. This pitch is determined, taking intoconsideration the width W1 of each lead 142 and the number of leads 142.For example, when the width W1 of the lead 142 is equal to or greaterthan 250 μm, but less than 300 μm, the pitch of leads 142 may be 4.75 to10.45 mm. When the width W1 of the lead 142 is equal to or greater than300 μm, but less than 350 μm, the pitch of leads 142 may be 4.75 to15.68 mm. When the width W1 of the lead 142 is equal to or greater than350 μm, but less than 400 μm, the pitch of leads 142 may be 4.75 to19.59 mm. When the width W1 of the lead 142 is equal to or greater than400 μm, but less than 500 μm, the pitch of leads 142 may be 4.75 to26.13 mm. In more detail, when the width W1 of the lead 142 is equal toor greater than 350 μm, but less than 400 μm, the pitch of leads 142 maybe 10.45 to 19.59 mm. When the width W1 of the lead 142 is equal to orgreater than 400 μm, but less than 500 μm, the pitch of leads 142 may be10.45 to 26.13 mm. Of course, the embodiments of the present inventionare not limited to the above-described conditions, and the pitch ofleads 142 and the pitch of bus bar lines 42 b may have various values.

In this embodiment, the first electrode 42, leads 142, electrode areaEA, edge area PA, etc., may be symmetrically arranged in a lateraldirection (a direction parallel to the finger lines 42 a) and a verticaldirection (a direction parallel to the bus bar lines 42 b or leads 142).In accordance with this arrangement, stable current flow may beachieved. Of course, the embodiments of the present invention are notlimited to the above-described arrangement.

As described above, a sufficient edge distance D is provided between oneend of each bus bar line 42 b (for example, an upper end of FIG. 9)and/or the other end of each bus bar line 42 b (for example, a lower endof FIG. 9) and the edge of the solar cell 150 adjacent thereto (namely,the first and/or second edge 161 or 162). Accordingly, the distancebetween both ends of the bus bar line 42 b in an extension direction ofthe bus bar line 42 b is shorter than the distance in the extensiondirection of the bus bar line 42 b between one outermost finger line 42a disposed at one-end side of the bus bar line 42 b (the uppermostfinger line in FIG. 9) and the other outermost finger line 42 a disposedat the other-end side of the bus bar line 42 a (the lowermost fingerline in FIG. 9) among the finger lines 42 a. Thus, effects of the edgedistance D may be sufficiently achieved.

The above description has been given mainly in conjunction with thefirst electrode 42 with reference to FIGS. 9 to 13. The second electrode44 may include finger lines, bus bar lines and edge lines respectivelycorresponding to the finger lines 42 a, bus bar lines 42 b and edgelines 42 c of the first electrode 42. The descriptions given of thefinger lines 42 a, bus bar lines 42 b and edge lines 42 c of the firstelectrode 42 may be applied to the finger lines, bus bar lines and edgelines of the second electrode 44 in a corresponding manner. As such, thedescription given of the first-conduction-type conductive region 20associated with the first electrode 42 may be applied to thesecond-conduction-type conductive region 30 associated with the secondelectrode 44 in a corresponding manner. The description given of thefirst passivation film 22, anti-reflective film 24 and openings 102associated with the first electrode 42 may be applied to the secondpassivation film 30 and openings 104 associated with the secondelectrode 44 in a corresponding manner.

The width, pitch, number, etc., of finger lines 44 a, the widths of lineand pad sections of bus bar lines 44 b and the pitch, number, etc., ofthe bus bar lines 44 b in the second electrode 44 may be equal to thewidth, pitch, number, etc., of finger lines 42 a, the widths of the lineand pad sections 421 and 422 of the bus bar lines 42 b and the pitch,number, etc., of the bus bar lines 42 b in the first electrode 42,respectively. Alternatively, the width, pitch, number, etc., of fingerlines 44 a, the widths of line and pad sections of bus bar lines 44 band the pitch, number, etc., of the bus bar lines 44 b in the secondelectrode 44 may differ from the width, pitch, number, etc., of fingerlines 42 a, the widths of the line and pad sections 421 and 422 of thebus bar lines 42 b and the pitch, number, etc., of the bus bar lines 42b in the first electrode 42, respectively. For example, the electrodesections of the second electrode 44, upon which a relatively smallamount of light is incident, may have a greater width than thecorresponding electrode sections of the first electrode 42 and a smallerpitch than the corresponding electrode sections of the first electrode42. Other variations are possible. Of course, the number and pitch ofthe bus bar lines 42 b in the first electrode 42 may be equal to thoseof the second electrode 44. In addition, the second electrode 44 mayhave a planar shape different from that of the first electrode 42. Othervariations are possible.

In accordance with this embodiment, it may be possible to minimizeshading loss through diffuse reflection, using the wire-shaped leads142. It may also possible to reduce the movement path of carriers byreducing the pitch of the leads 142. Accordingly, efficiency of thesolar cell 150 and output power of the solar cell panel 100 may beenhanced. In addition, it may be possible to enhance attachment forcebetween each wire-shaped lead 142 and the first electrode 42 by definingthe edge distance D of the first electrode 42 in accordance with thewidth of the lead 142. Accordingly, damage to the solar cell 150 or thelike, which may occur due to separation of the lead 142 from the firstelectrode 42, may be prevented and, as such, the solar cell 150 may havesuperior electrical characteristics and reliability. In addition, it maybe possible to maximize output power of the solar cell panel 100 bydefining the number of leads 142 in accordance with the width W1 of eachlead 142.

Hereinafter, a solar cell according to another embodiment of the presentinvention and a solar cell panel including the same will be describedwith reference to the accompanying drawings. The above description maybe applied to parts identical or similar to those described above in thesame manner and, as such, no description will be given of the identicalor similar parts, and only parts different from those described abovewill be described in detail. Combinations of the above-describedembodiment, variations thereof, and the following embodiments andvariations also fall within the scope of the embodiments of the presentinvention.

FIG. 14 is a plan view illustrating a portion of the front surface of asolar cell according to another embodiment of the present invention.

Referring to FIG. 14, the solar cell may include line breaking sectionsS, at which finger lines 42 a arranged between two neighboring bus barlines 42 b are broken at respective parts thereof without extendingcontinuously.

In this instance, the line breaking sections S may be formed at thefinger lines 42 a arranged in the first electrode areas EA1,respectively, and may be not formed at the finger lines 42 a arranged inthe second electrode areas EA2. Although the finger lines 42 a in eachfirst electrode area EA1 have respective line breaking sections S,current may smoothly flow through the finger lines 42 a because thefinger lines 42 a are connected to two neighboring bus bar lines 42 b orleads 142 at opposite sides thereof. In this instance, accordingly, itmay be possible to reduce the area of the first electrode 42 withoutobstructing flow of current in the first electrode area EA1 and, assuch, manufacturing costs and shading loss may be reduced. On the otherhand, the finger lines 42 a in each second electrode area EA2 areconnected to one bus bar line 42 b or lead 142 only at one side thereof,and have no line breaking section S and, as such, current may smoothlyflow to the bus bar line 42 b or lead 142 disposed at one side of thefinger lines 42 a.

The line breaking sections S of the finger lines 42 a in each firstelectrode area EA1 may be centrally arranged between two neighboring busbar lines 42 b corresponding to the first electrode area EA1.Accordingly, it may be possible to minimize a current movement path.

The width of each line breaking section S may be 0.5 times or more thepitch of each finger line 42 a, and may be 0.5 times or less the pitchof each bus bar line 42 b. When the width of each line breaking sectionS is less than 0.5 times the pitch of each finger line 42 a, effects ofthe line breaking section S may be insufficient because the linebreaking section S is too narrow. On the other hand, when the width ofeach line breaking section S is greater than 0.5 times the pitch of eachbus bar line 42 b, electrical characteristics may be degraded becausethe line breaking section S is too wide. For example, the width of theline breaking section S may be 1.5 to 1.8 mm. Meanwhile, for example,the width of each line breaking section S may be greater than the widthW6 of each pad section 422 in each bus bar line 42 b. Within this range,effects of the line breaking section S may be maximized. Of course, theembodiments of the present invention are not limited to theabove-described conditions, and the width of each line breaking sectionS may have various values.

The ratio of the number of finger lines 42 a having line breakingsections S in each first electrode area EA1 may be 0.33 to 1 times thetotal number of finger lines 42 a in the first electrode area EA1 whenthe numbers of the finger lines 42 a are measured in a directionparallel to the bus bar lines 42 b. Within this range, effects of theline breaking section S may be maximized. For example, in thisembodiment, in each first electrode area EA1, finger lines 42 aconnecting two neighboring lines 42 b and finger lines 42 a having linebreaking sections S are alternately arranged one by one. In thisinstance, accordingly, it may be possible to minimize the averagemovement distance of carriers while providing a sufficient number ofline breaking sections S. Of course, the embodiments of the presentinvention are not limited to the above-described conditions, and theabove-described number ratio may be varied.

Although the line breaking sections S are illustrated in FIG. 14 asbeing provided at each first electrode area EA1, the embodiments of thepresent invention are not limited thereto. The line breaking sections Smay be provided at a part of the plurality of first electrode areas EA1,and may be not provided at the remaining part of the plurality of firstelectrode areas EA1. In the drawings and above description, althoughillustration and description has been given in conjunction with thefirst electrode 42, the description may be applied to the secondelectrode 44 in the same manner.

FIG. 15 is a plan view illustrating a portion of the front surface of asolar cell according to another embodiment of the present invention.

Referring to FIG. 15, the solar cell may include finger lines 42 a eacharranged between two neighboring bus bar lines 42 b while havingportions having different line widths. Each of the finger lines 42 a mayinclude a narrow portion S1 having a relatively small width, and a wideportion S2 having a relatively great width.

For example, in this embodiment, each of the finger lines 42 a arrangedin each first electrode area EA1 may include a narrow portion S1 and awide portion S2, and each of the finger lines 42 a arranged in eachsecond electrode area EA2 has a uniform width (for example, a widthequal to that of the wide portion S2). In the first electrode area EA1,current may smoothly flow because the finger lines 42 a are connectedbetween two neighboring bus bar lines 42 b or leads 142. Accordingly, itmay be possible to reduce the area of the first electrode 42 by virtueof the narrow portions S1 of the first electrode 42 without obstructingflow of current and, as such, manufacturing costs and shading loss maybe reduced. On the other hand, in the second electrode area EA2, thefinger lines 42 a are connected to one bus bar line 42 b or lead 142only at one side thereof, and have a uniform width because no narrowportion S1 is provided and, as such, current may flow to the bus barline 42 b or lead 142 disposed at one side of the finger lines 42 a.

In this embodiment, the narrow portions S1 of the finger lines 42 a maybe centrally arranged between two neighboring bus bar lines 42 b, andthe finger lines 42 a may have a width gradually increasing toward thetwo neighboring bus bar lines 42 b. Accordingly, smooth current flow maybe achieved. Of course, the embodiments of the present invention are notlimited to the above-described conditions, and the finger lines 42 aeach having the narrow portion S1 and wide portion S2 may have variousshapes.

The ratio of the number of finger lines 42 a having narrow portions S1in each first electrode area EA1 may be 0.33 to 1 times the total numberof finger lines 42 a in the first electrode area EA1 when the numbers ofthe finger lines 42 a are measured in a direction parallel to the busbar lines 42 b. Within this range, effects of the line breaking sectionS may be maximized.

Although the narrow portions S1 are illustrated in FIG. 15 as beingprovided at each first electrode area EA1, the embodiments of thepresent invention are not limited thereto. The narrow portions S1 may beprovided at a part of the plurality of first electrode areas EA1, andmay be not provided at the remaining part of the plurality of firstelectrode areas EA1. In addition, the line breaking section Sillustrated in FIG. 14 may be provided in combination with the narrowportion S1. In the drawings and above description, although illustrationand description has been given in conjunction with the first electrode42, the description may be applied to the second electrode 44 in thesame manner.

Hereinafter, the embodiments of the present invention will be describedin more detail with reference to an experimental example according tothe present invention. The following experimental example is onlyillustrative for reference and, as such, the embodiments of the presentinvention are not limited thereto.

Experimental Example

A lead having a circular cross-section and a width of 300 μm wasattached to a solar cell having an edge distance of 7.5 mm. Attachmentforce was then measured while pulling the lead using an experimentaldevice (for example, a tensile testing device). The measured values ofattachment force are depicted in FIG. 16.

In FIG. 16, the horizontal axis represents distance, and the verticalaxis represents attachment force. The horizontal axis may be dividedinto three sections. The first section, namely, a section I, is asection in which pulling of the lead is begun, and is continued beforethe lead is tightened. The second section, namely, a section II, is asection in which the lead is actually tightened by the experimentaldevice in accordance with pulling. The third section, namely, a sectionIII, is a section in which the lead is detached from pad sections.Accordingly, actual attachment force may be measured in the secondsection II.

In the first section I, no actual force is applied to the lead becausethe first section I is a small-distance section.

In the second section II, the experimental device continuously pulls thelead. Accordingly, as the distance in the second section II increases,stress applied to the lead is increased in proportion to distance. Thus,the graph in FIG. 16 depicts gradual increase of attachment force towardan apex. In more detail, attachment force gradually increases in thesecond section II, and then abruptly decreases after passing an apex of2.058N.

The third section III is a section following the apex of attachmentforce. In the third section III, stress applied to the lead is abruptlyreduced because the lead is detached from first pad sections.

It may be seen that attachment force of the lead according to thisembodiment exhibits a superior value of 2.058N.

The features, structures, effects, etc., as described above are includedin at least one embodiment, and are not limited to a particularembodiment. In addition, although the example embodiments of the presentinvention have been disclosed for illustrative purposes, those skilledin the art will appreciate that various modifications, additions andsubstitutions are possible, without departing from the scope and spiritof the invention as disclosed in the accompanying claims.

What is claimed is:
 1. A solar cell comprising: a semiconductorsubstrate; a conductive region disposed in or on the semiconductorsubstrate; and an electrode comprising a plurality of finger linesconnected to the conductive region, and formed to extend in a firstdirection while being parallel, and 6 or more bus bar lines formed toextend in a second direction crossing the first direction, each of thebus bar lines having a width of 35 to 350 pm at at least a portionthereof, wherein the each of the bus bar lines has a distance betweenopposite ends thereof in the second direction smaller than a distancebetween outermost ones of the finger lines respectively disposed atopposite sides of the semiconductor substrate in the second direction,wherein the each of the bus bar lines comprises a plurality of padsections arranged to be spaced apart from one another in the seconddirection, wherein the plurality of pad sections comprise: first padsections having a length in the second direction greater than a width ofthe plurality of finger lines, wherein the first pad sections aredisposed at the opposite ends of the bus bar lines in the seconddirection, and second pad sections having a length in the seconddirection greater than the width of the plurality of finger lines, andthe length in the second direction smaller than the length in the seconddirection of the first pad sections, wherein a distance between thefirst pad sections and an edge of the solar cell adjacent thereto isgreater than a distance between the outermost ones of the finger linesand the edge of the solar cell adjacent thereto, wherein an edge area isdefined between one end of one of the bus bar lines and the edge of thesolar cell adjacent thereto or between the other end of the one of thebus bar lines and the edge of the solar cell adjacent thereto, whereinthe edge area includes: first edge areas defined between neighboringfinger lines, second edge areas corresponding to a remaining portion ofthe edge area except for the first edge areas, and being defined betweenthe outermost ones of the finger lines and the edge of the solar celladjacent thereto, wherein a lead is disposed in the first edge areas,and is space apart from the edge of the solar cell adjacent thereto, andwherein the first pad sections are disposed adjacent to the first edgeareas, wherein when “L” represents a width of the edge area at aposition adjacent to a corresponding one of the edges of the solar cell,and “D” represents an edge distance being a length of the edge area, “L”and “D” satisfy the following Expression:0.9*(0.1569*D+0.3582)<L<1.1*(0.1569*D+0.3582)  <Expression> where, theunit of “L” is mm, and the unit of “D” is mm.
 2. The solar cellaccording to claim 1, wherein: the 6 or more bus bar lines have a firstdistance between two neighboring ones of the bus bar lines, and a seconddistance between one of the bus bar lines adjacent to an edge of thesolar cell and the edge of the solar cell, the second distance beinggreater than the first distance; and an edge distance is defined betweenone end of the one of the bus bar lines and the edge of the solar celladjacent thereto or between the other end of the one of the bus barlines and the edge of the solar cell adjacent thereto, the edge distancebeing smaller than the first distance and the second distance.
 3. Thesolar cell according to claim 1, wherein each of the bus bar linesfurther comprise a line section connecting the plurality of pad sectionsin the second direction while having a smaller width than the pluralityof pad sections.
 4. The solar cell according to claim 3, wherein thefirst pad sections and the second pad sections have different widths inthe first direction.
 5. The solar cell according to claim 4, wherein:the width in the first direction of the first pad sections is greaterthan the width in the first direction of the second pad sections; andthe first pad sections are disposed at opposite ends of the line sectionin the second direction, respectively.
 6. The solar cell according toclaim 1, wherein an edge distance of 2.37 to 21.94 mm is defined betweenthe one end of the one of the bus bar lines and the edge of the solarcell adjacent thereto or between the other end of the one of the bus barlines and the edge of the solar cell adjacent thereto.
 7. The solar cellaccording to claim 6, wherein the edge distance is 9 to 15.99 mm.
 8. Thesolar cell according to claim 1, wherein the edge area has a width of0.73 to 3 mm at a position adjacent to a corresponding one of the edgesof the solar cell.